Power occasionally comes with a price.
Getting your brains blasted with enough magic to make manehattan glow for a decade is a small price to pay for being an alicorn.
It's still a price, though. It comes with drawbacks.
Twilight Sparkle's still trying to learn to deal with it.

Pre-read by The 24th Pegasus and Door Belle. Go check out their works, they're cool dudes.