"Certainty about the future is a sign of mental illness." (NOTE: There's a second lesson here about "we shall (not) be vindicated".)
Why? Because only the self-delusional are absolutely certain about anything... including the future. And self-delusion is a mental illness.
Therefore, thinking only positive thoughts about yourself (well beyond what's needed for self-esteem) and your future is also self-delusion.
But wait, you say, are you saying that I can't give myself a compliment? A thumbs up to myself in the mirror?
No, I didn't say that. Going OVERBOARD with such compliments to the point of ignoring reality is dangerous, and so are anyone trying to dissuade you from reality.
But to explain that, we need to explain how the brain works when it comes to social interactions.