One of the principles i thought for my stories' fundamental forces is Universal Inertia.
the idea runs similar to non-newtonian fluids: the more pressure you put on moving it, the harder it gets. That is, the greater the magical change, the more energy needs to be put to actually do it.
the trick with it is to learn to be softer, slower, let it flow, dont put pressure, just movement.
a novice to magic might try to put all their strenght into casting a small spell, and it works, but it will be very exausting on the long term. As they develop their knowledge, they learn how to do things with less force.
an example would be trying to create a Sourceless flame.
Even sparks may be hard for a young mage, its efforts concentrated yet almost fruitless in producing fire.
Then they keep practicing.
The sweat of their brow dripping day by day, each day a bit closer to their objective. they learn how the flame works, how they start and sustain themselves.
It becomes easier, the sparks now hold a consistent fire, its light flickering in the wind like a candle. they can now gently move it, as if held by a lamp.
Their work progresses, their flame grows in strenght and light, and yet, easier than ever, their ability now can move it freely with their hands, as if a toy ball, the heat only a warm touch, but a piece of inferno to any others around.
Months and months of work paid off, now a pyromancer, fire follows his steps, rooms light up with his presence, a soft warmth emanating from his whole figure, the dim sparks of years ago now a second nature to him.
I dont think there is a limit on what you can do with it, But its use comes with a very heavy toll on both mind and body. it gets easier, but even having knowledge and mastery of one doesnt guarantee faster learning of another.
An already accomplished mage may have an easier time picking up a new type of spell, but they will always start a few steps behind. Hell, some may have a harder time learning certain spells specifically because of their experience with another one.


