If you feel below par now, don't think your life is deserting you forever. You are just as sure to be up again as you are, when elated, sure to be down again. Six months, or any given cycle of time, is sure to see you produce a certain amount, and your fretful anxiety when in a stagnant mood is frivolous. The good time will come again, as it has come; and go too. I think we ought to be independent of our moods, look on them as external, for they come to us unbidden, and feel if possible neither elated nor depressed, but keep our eyes upon our work and, if we have done the best we could in that given condition, be satisfied.

~ from a letter written by William James to his friend, Tom Ward, June 8, 1866 ~