In my D&D game, the spell wish doesn't work after you cast it a certain amount of times.
The relevant portion of the wish description (emphasis mine):
Finally, there is a 33 percent chance that you are unable to cast wish ever again if you suffer this Stress.
Imagine an ocean, infinitely big, that exists above the Material Plane. That ocean is the Weave, and it is full of magic. That ocean has a thousands of little streams of magic, called Souls, that connects every living being to the Weave. The Weave is too far away for any mortal being too use, but the Soul is easily accessible. When a person uses magic, they draw on the power of the Soul. Powerful wizards have essentially widened their Soul by using so much magic it erodes the "riverbank", and as such can use much more magic in their souls.
Essence is what the universe thinks of you; what YOU are. Imagine a paragraph, that describes every facet of who you are. What you think, how you look, everything. Using powerful magic, you can change something's essence. The more you change something's essence, the more Mana it requires.
When you cast a spell, you draw on the power of your Soul in order to change the universe. The larger the change, the more magic it requires, and so people's magical ability is limited by the power of their soul.
How Wish Works
When you cast Wish, you create essentially an incredibly powerful transmitter, which sends a signal to the Weave. This signal tells the Weave what you want it to do, and as such Wish can do incredibly powerful magic.