Note: This is meant to be a fun thread, I certainly don't expect all dms to consider spells this way, and its certainly not meant to be a thread that declares "if your not considering spells this way your wrong". Its just light-hearted and fun.
If we imagine that the mechanics of spellcasting are truly how spellcasters in the fantasy world operate, we can actually infer a fair amount about how spellcasting actually "works". Lets dig in and see what we can glean.
Casting a spell is NOT an exact science
This is infered by the simple fact that spellcasting doesn't have a failure chance in the vast majority of cases. A 1st level wizard can be crawling away from a balor on their hands and knees, breathless and winded, and yet have no failure chance for a spell.
This suggests that the mechanics of spellcasting might be exotic, but they aren't exact. The hand motions don't have to be perfectly precise; the sounding of the words doesn't have to be pitch perfect. Close is close enough in horseshoes and in spellcasting.
There's something weird about Armor and Magic
So if we go with the above assumption...than there is something weird about armor, something that completely stops spellcasting. There are some many other things that don't impact spellcasting, than why armor?
The normal arguments of "it hinders motion" don't really hold water, as sorcerers still have the problem even with careful spell as an example. and we've already shown that all sorts of crazy things that you would think hinder motion spellcasters have 0 problem with.
This suggests that armor somehow hinders the "energy flow" of a spell's magic, and perhaps the reason a caster needs proficiency is that they actually learn alternate ways they have to channel the magic to make it work in armor.
Sorcerers have an innate "sense" of how their magic works
While some sorcerers might have tutors, there is no requirement of that in dnd terms. And yet sorcerers somehow manage to learn the right words to say, hand motions to use, and know they need to grab the bat guano to make their fireballs work.
This suggests that sorcerers have some innate intuition to their magic, that they "know" how to cast their spells in a way that doesn't require tutoring or external learning. Maybe its a voice that whispers to them, maybe they get a mental ping to store that bat guano they just passed, or xyz.
Different classes cast spells "differently."
This might be obvious, but the spell identification rules in Xanathar's mention that you get advantage on identifying a spell if the caster is the same class as you are. This suggests that something about the way a casting class casts their spell is innately different from one other, enough to give an effective +5 on the identification check.
Concentration is as much "physical" as "mental"
While we often think of concentration as a mental act, mechanically the effect is as much physical as anything. Constitution is mainly a physical stat first and foremost.
Then there is the fact that I can engage in many complex mental tasks while maintaining concentration. I can even cast most other spells, or prepare and entirely new suite of spells all while concentrating on a spell.
And lastly, paralyzing stops concentration even though the person is still capable of mental thoughts, they are only physically stopped.
This suggests that concentration almost creates an "ongoing effect" within the caster's body, and that only disruptions of that effect is what actually breaks concentration. This ongoing effect is not really something the caster has to "maintain" that much, again which explains why they can do so many other complex activities while concentrating, but if its disrupted, the caster may have to do some activities to "settle" the flow (aka the concentration check). It also might explain why you can only concentrate on one spell at a time, again its not so much the mental effort (casters can do plenty of complex mental things while concentrating on a spell), its more that you can't have more than one "energy flow" going on in the body at one time. You can't cross the streams so to speak.
"Perception of Space" is a very important focus in Magic
When it comes to spells, having to see something in order to use magic is more the rule than the exception. The vast majority of spells requires a caster to see something to make magic happen.
However, actual "sight" is not needed. Secondary sights like tremorsense are sufficient. So its less the true act of sight as it is a perception of the space around you, being able to concretely know a spot near you and direct the magic to that spot. This seems to be an important focus point for many magics.
Most Spell Components are a "circuit" rather than an "ingredient".
A more recent change with 5e. In 5e, the vast majority of material components are in fact not consumed by the spell (not even fireball!). Further, they can be readily replaced by a spellcasting focus.
This suggests that the magic doesn't require any "energy" from the ingredient itself, but rather its more like a circuit, the ingredient in some way completes the circuit of magical energy needed for the spell to function, which can be mimiced with a spell casting focus.
(Greater Speculation) Wizards learned the first magics from clerics and sorcerers.
This is more speculation than most of the facts. It comes from the simple fact that, when you include various cleric domains, clerics have access to a good amount of common arcane spells. Sorcerers also have access to the majority of spells wizards can cast. Considering the age of the gods in most settings, and that wizards had to "learn" how to do magic through research....it highly likely that wizards started learning magic from clerics.
A light domain cleric casts fireball, and a wizard through intense study of magic learned to replicate the effect. likewise, an innate magical caster like a sorcerer was likely a wonder to the first arcane studies of magic. They would likely study the hand motions and words of sorcerers to get the first gleans into how to make magic work in other ways.
Water doesn't hinder magic
Many of our above notes suggests an "energy flow" to magic. Whatever that flow is, it runs through water just fine. A caster can cast in water (though they might need air to cast their Verbal components). Concentration spells work fine in water, etc.
So what other interesting flavor ideas can we gleen from the mechanics of spellcasting?
If we imagine that the mechanics of spellcasting are truly how spellcasters in the fantasy world operate, we can actually infer a fair amount about how spellcasting actually "works". Lets dig in and see what we can glean.
Casting a spell is NOT an exact science
This is infered by the simple fact that spellcasting doesn't have a failure chance in the vast majority of cases. A 1st level wizard can be crawling away from a balor on their hands and knees, breathless and winded, and yet have no failure chance for a spell.
This suggests that the mechanics of spellcasting might be exotic, but they aren't exact. The hand motions don't have to be perfectly precise; the sounding of the words doesn't have to be pitch perfect. Close is close enough in horseshoes and in spellcasting.
There's something weird about Armor and Magic
So if we go with the above assumption...than there is something weird about armor, something that completely stops spellcasting. There are some many other things that don't impact spellcasting, than why armor?
The normal arguments of "it hinders motion" don't really hold water, as sorcerers still have the problem even with careful spell as an example. and we've already shown that all sorts of crazy things that you would think hinder motion spellcasters have 0 problem with.
This suggests that armor somehow hinders the "energy flow" of a spell's magic, and perhaps the reason a caster needs proficiency is that they actually learn alternate ways they have to channel the magic to make it work in armor.
Sorcerers have an innate "sense" of how their magic works
While some sorcerers might have tutors, there is no requirement of that in dnd terms. And yet sorcerers somehow manage to learn the right words to say, hand motions to use, and know they need to grab the bat guano to make their fireballs work.
This suggests that sorcerers have some innate intuition to their magic, that they "know" how to cast their spells in a way that doesn't require tutoring or external learning. Maybe its a voice that whispers to them, maybe they get a mental ping to store that bat guano they just passed, or xyz.
Different classes cast spells "differently."
This might be obvious, but the spell identification rules in Xanathar's mention that you get advantage on identifying a spell if the caster is the same class as you are. This suggests that something about the way a casting class casts their spell is innately different from one other, enough to give an effective +5 on the identification check.
Concentration is as much "physical" as "mental"
While we often think of concentration as a mental act, mechanically the effect is as much physical as anything. Constitution is mainly a physical stat first and foremost.
Then there is the fact that I can engage in many complex mental tasks while maintaining concentration. I can even cast most other spells, or prepare and entirely new suite of spells all while concentrating on a spell.
And lastly, paralyzing stops concentration even though the person is still capable of mental thoughts, they are only physically stopped.
This suggests that concentration almost creates an "ongoing effect" within the caster's body, and that only disruptions of that effect is what actually breaks concentration. This ongoing effect is not really something the caster has to "maintain" that much, again which explains why they can do so many other complex activities while concentrating, but if its disrupted, the caster may have to do some activities to "settle" the flow (aka the concentration check). It also might explain why you can only concentrate on one spell at a time, again its not so much the mental effort (casters can do plenty of complex mental things while concentrating on a spell), its more that you can't have more than one "energy flow" going on in the body at one time. You can't cross the streams so to speak.
"Perception of Space" is a very important focus in Magic
When it comes to spells, having to see something in order to use magic is more the rule than the exception. The vast majority of spells requires a caster to see something to make magic happen.
However, actual "sight" is not needed. Secondary sights like tremorsense are sufficient. So its less the true act of sight as it is a perception of the space around you, being able to concretely know a spot near you and direct the magic to that spot. This seems to be an important focus point for many magics.
Most Spell Components are a "circuit" rather than an "ingredient".
A more recent change with 5e. In 5e, the vast majority of material components are in fact not consumed by the spell (not even fireball!). Further, they can be readily replaced by a spellcasting focus.
This suggests that the magic doesn't require any "energy" from the ingredient itself, but rather its more like a circuit, the ingredient in some way completes the circuit of magical energy needed for the spell to function, which can be mimiced with a spell casting focus.
(Greater Speculation) Wizards learned the first magics from clerics and sorcerers.
This is more speculation than most of the facts. It comes from the simple fact that, when you include various cleric domains, clerics have access to a good amount of common arcane spells. Sorcerers also have access to the majority of spells wizards can cast. Considering the age of the gods in most settings, and that wizards had to "learn" how to do magic through research....it highly likely that wizards started learning magic from clerics.
A light domain cleric casts fireball, and a wizard through intense study of magic learned to replicate the effect. likewise, an innate magical caster like a sorcerer was likely a wonder to the first arcane studies of magic. They would likely study the hand motions and words of sorcerers to get the first gleans into how to make magic work in other ways.
Water doesn't hinder magic
Many of our above notes suggests an "energy flow" to magic. Whatever that flow is, it runs through water just fine. A caster can cast in water (though they might need air to cast their Verbal components). Concentration spells work fine in water, etc.
So what other interesting flavor ideas can we gleen from the mechanics of spellcasting?