No slave to vulgar moods: A great person is never the victim of passing fancies. This is a good precept to meditate upon yourself, to discover your present mood and to prepare against it. Or even to throw yourself into an opposite one, in order to come to rest between the natural and the assumed, on the balance point of common sense. It is a principle that in order to improve yourself, you must first know yourself. For there exist veritable monsters of moodiness, always of a different temper, and of a different mind with each. Eternally enslaved by their smug intemperance, they involve themselves most consistently, their excess checkmating not only their purpose but attacking their judgement, thus defeating both their ends and their plan.
~ Baltasar Gracian, The Art of Worldly Wisdom (1647)