We all do things simply because we feel we "should." Maybe you volunteer because a friend asked you to, but you feel no real connection to the cause you support. Maybe you have a weekly lunch with some old friends, but it feels more like a chore than a treat. Or maybe you keep trying to learn French just because once you started you didn't want to feel like a quitter.
Think about one thing you do out of habit, or because you think you're supposed to, or simply because you don't know how to get out of it--and then get out of it.
The momentary pain (or, in some cases, confrontation) that results from stepping down, dropping out, or letting go will be quickly be replaced by a huge sense of relief. And you can use the time you save to do something you feel has real meaning.