There are some great roles - mostly in Shakespeare's tragedies which no one can play at full strength from beginning to end. One simply hopes that one can hit the peaks as often as one has the strength.
Think positively and masterfully, with confidence and faith, and life becomes more secure, more fraught with action, richer in achievement and experience.
The chemist who can extract from his heart's elements compassion, respect, longing, patience, regret, surprise, and forgiveness and compound them into one can create that atom which is called love.