Always Look on the Sunny Side of Life

I'm doing reading for my Social Psychology class, and right now I'm learning about self-fulfilling prophecies. It's something I've studied before in other psych classes, and it's pretty interesting. Basically, in Psychology, a self fulfilling prophecy is when you have an expectation about a person or a situation, so you alter your behavior (often unconsciously) according to your expectations, thus evoking exactly the behavior or experiences that you expected.

An example:
In one study, school teachers were told that a few of their students had done exceptionally well on a standardized test and that those students were likely to excel academically. Throughout the year, teachers paid those students more attention, allowed them more time to ask questions, and encouraged them to try more difficult assignments. By the end of the year, those students were outperforming many of their classmates. However, no standardized test results were ever actually found. It was the teacher's expectations that the students would excel that helped them do so.

Obviously, not everything in life is a self-fulfilling prophecy, and sometimes our expectations turn out to be true simply because they are true. However, cases like this make me wonder if people who have positive outlooks on life really are going about it in the right way. If we always tell ourselves that every new person we meet will be kind, worth talking to, and interesting, perhaps it will be more likely that they will behave in that way. It seems to me that maybe people had the right idea when they said "think positively!"