Perhaps it's about hope. If you get your hopes up, then there is a chance you will be let down by life. As for positive thinking, I would say that positive thinking doesn't equal positive outcomes. Or what I mean is, positive thinking doesn't always return a positive result but positive thinking can give you a big boost in trying to obtain a positive result. Sports comes to mind but the same can apply to other things in life and to life in general.

If don't have any positivity within you, then its going to be harder to achieve things or obtain goals. Positivity gives you that extra bounce and lift.