This is best illustrated by the Pygmalion Effect Study. In 1966, Harvard professor Robert Rosenthal and Lenore Jacobson, a primary school principal in California, contacted teachers in a primary school and asked if they could administer an IQ test to all students. Although they didn't share the test scores with teachers, they mentioned some students appeared to be “intellectual bloomers” who might start to outperform classmates. The teachers were given the names of these supposedly promising students, who had been selected at random. Eight months later, Rosenthal and Jacobson retested all the students. Those they'd pointed out as “intellectual bloomers” had made larger IQ gains. Rosenthal and Jacobson speculated that teachers, probably without realising it, had begun to behave more positively to the “promising” students, paying them more attention and praising their success. There have been some quibbles about the methodology, but other publications upheld the overall findings.

This has profound implications for us. Everyone you know will have both desirable and undesirable characteristics. However, it's up to you which of those characteristics you choose as your focus. If you concentrate on what you don't like, you're likely to feel irritated when you're around them, and to avoid them whenever you can. If you decide to focus on those qualities you like about that individual, they're likely to repeat the behaviours that gained your approval. 

The lesson? If you choose to focus on the positive qualities you find in others, then everyone wins. 

Linda Blair, The Telegraph