Rejection therapy has its ideological roots in Stoicism, just as the central ideas of this article does. Seneca talks about spending a few days each month wallowing in the things that you fear the most, so that they can't control you.

And with regard to the anti-fragility thing, this is discussed at length also in Letters from a Stoic. Seneca talks about not being overly dominated by your fears, but also you can be a slave to hope as well. The idea of being happy and free when poor, and cautious when prosperous is also straight out of stoicism.

When I read Seneca in Letters from a Stoic, I get the impression that he's a mental martial arts master, constantly training to be in control of his mind and his happiness, always pursuing excellence.

http://www.fourhourworkweek.com/blog/2009/04/13/stoicism-101...