"Our foolish naive persistence defied what many thought impossible -- what I had thought was impossible." - Natasha Lance Rogoff, Muppets in Moscow.
Is that all you need to defy the odds? Yes.
All that you have is the present. In this present you can decide to start, stop, or continue. The present doesn’t care if you give up or slog through life; the present doesn’t know past or future. The present knows what you do now.
I don’t know what the future holds — perhaps that’s naive. I know that what I do now sets the stage for what’s to come. If I want to be more than what I think I am, I must decide and act that way now.