Discipline is doing what you DON'T want to do when you DON'T want to do it because it NEEDS to be done. On the flip side,discipline is NOT doing what you DO want to do when you DO want to do it because it should NOT be done.

Example of the first one: cleaning the bathroom.

Example of the second one: snacking when you're not hungry as a way to procrastinate a challenging or distasteful task.