Guilt. From eating too much at dinner, skipping a workout, flaking on a friend who needed you, messing up at work, whatever. What allows you to bounce back from the negativity?
What helps you work through feelings of guilt? And how do you think guilt is tied in to everyday behaviors and routines?
There's nothing but time and trying to make amends on your mistakes. Also try to accept what happened and that it's okay to not be perfect.