Discipline is having the strength to do a good work in spite of a negative emotion.
Perfectionism is idolatry of a plan (even a good one). Its seed produces impatience, frustration, a burdened heart, and discontentment, not only in the perfectionist but in the family and friends around them. It makes one's faith odious.
Like St Paul, we are set free to be profoundly, peacefully, joyfully content in all circumstances. Not with all circumstances, to be sure, but in all circumstances. Perfectionism is making our righteousness the god and the goal, instead of enjoying Christ's goodness as our mainstay and dear delight.