As Jonathan Creek said:

We mustn't confuse what's impossible with what's implausible.

Success might be implausible - unlikely or improbable. But that's very different to say that it can never ever happen. For a long time I thought that completing my PhD was impossible. Then, I thought it was improbable. Then, despite all of this, I did it anyway!

That, and being flexible about how you measure success helps too. Not everything worth doing - either for yourself or others - can be measured purely in fame and fortune (but I would say that).