This is a great question for trainerboy. Where are you trainerboy? iSteve is right im that our words can shape our reality plus, in general, people respond better to others that are uplifting and positive.
I haven’t observed this; it seems to me that the truth of the statement matters more than positive or negative. Some of the worst people to deal with are the ones who are always positive, even if they have to lie to do it.
Mostly people take actions or stop themselves based on what they’re thinking and expecting, rather than on what’s real. So yes, people shape their experiences of the world from day to day and from moment to moment, to a far greater degree than most of us believe. We also get tied up in self-deception, as cwilbur pointed out with his example of false positive assertions – they do create… false positiveness.