If he has strong emotions naturally, his problem is to check, guide, and rule them where they are of the lower human kind. But of course, the highest and noblest emotions need not be checked, and he may safely give himself up to them. He must get a better balance of temperament by disciplining his feelings, cultivating the moments of calmness which come to him, and by developing the reasoning faculty. He should also practise the exercise of constantly thinking over his past. But his thoughts should be tranquil, impersonal, self-critical, and he should be eager to learn the lessons to be gained from this practice. Especially should he look for the mistakes made, the faults displayed, and--by studying the results to which they led--try to get rid of these weaknesses of character.
-- Notebooks Category 6: Emotions and Ethics > Chapter 3: Discipline Emotions > # 84