Magic

Reality resembles a vast network of invisible threads. All magic alters this weave, but the price of that change does not depend only on the strength of the effect.

Imagine trying to cut a single thread with a blunt blade. The effort makes the entire network vibrate. Those vibrations return to the caster as a backlash known as Momentum.

Now imagine a perfectly sharp blade. It can cut several threads at once without disturbing the surrounding network. The change is greater, but it encounters less resistance.

For this reason, some simple magic can generate considerable Momentum, while other, far more powerful magic produces no backlash at all. The determining factor is not the magnitude of the change to reality, but how that change is made.

Magic is limited not by what the caster wishes to accomplish, but by their ability to act in harmony with the threads of the world.