You are a reasoning animal. So what is the good in you? Perfect reason. So call it back on duty to pursue its goal, and let it grow abundantly, as much as it is able. Then judge that you are blessed, when all your joy comes to you from yourself, when after seeing what men snatch, long for, and keep under guard you find nothing—I won’t say that you would prefer—but nothing you would even want. I will give you a short rule of thumb by which to measure yourself, by which you will perceive that you are now perfect: you will have your own good when you understand that the successful are the most unsuccessful. Keep well.

From Seneca’s Letter 124 (Book XX) in Selected Letters, translation by Elaine Fantham, Oxford: Oxford University Press, 2009, p. 274.