In the bestselling The Four: The Hidden DNA of Amazon, Apple, Facebook, and Google, New York University-academic and business analyst Scott Galloway advices taking things in stride:

Nothing is ever as good or bad as it seems. All situations and emotions pass. When you have a big victory, pull in your horns and be risk avoidant for a period. Regression to the mean is a powerful force, and the good luck (and a lot of it is luck) will cut the other way at some point. So, many entrepreneurs who make a lot of money on one venture turn around and lose a lot of it because they believe the victory was due to their genius and they should go bigger. At the same time, when beaten down, realize you are not as stupid as the world, at that moment, seems to think you are. When beaned in the face, the key is to get up, dust off, and swing harder.