Is Willpower Really a Muscle?
The ego depletion theory is on shaky ground
The idea that willpower works like a muscle, that you have a limited supply that gets 'depleted' with use, was one of the most influential psychology theories of the 2000s. It's called ego depletion, and it was incredibly intuitive. But when researchers tried to replicate the key studies with larger samples and stricter methods, the effect largely vanished. The theory is now on very shaky ground.
In real life...
Instead of thinking of willpower as a draining battery, focus on building habits and environments that reduce the need for self-control in the first place. Put the cookies out of sight, lay out your gym clothes the night before, and use implementation intentions, 'when X happens, I will do Y.' Design your life so willpower is a backup, not your primary strategy.