I think your example is not suitable for situation above - there I can see only two possible outcomes: X happen or X not happen. We don't know anything more about X. And P(X|A) + P(X|~A) = 1, isn't so?
Sorry, I don't understand - why does sum of probabilities not equal 100% in your example? Assume that you missed "5" in "P(X|I believe X won't happen) = 1%"
Perhaps I would be better off being deluded about it.
But for what reason?
I think that great example of growth mindset is "Baby steps" anime and manga (http://mangafox.me/manga/baby_steps/). Boy become proffesional tennis player from scratch using deliberate practice and hard work.