[F]ortune does not know how to be inactive; she enjoys substituting sorrow for happiness, or at least mixing the two.  So, no one should be confident in times of success, nor give up in times of adversity.  The changes of fortune alternate.  Why do you rejoice?  Those very circumstances which have carried you to the heights will abandon you, you know not where.  They will have their end, not yours.  Why are you despondent?  You have been carried down to a low point, but now is the time to rise again.  Failure changes for the better, success for the worse. 

Seneca, Naturale Quaestiones, Book III