The tricky thing about your expectations is that they impact other people too. As far back as the 1960s, Harvard research demonstrated the power of our beliefs in swaying other people’s behavior. When teachers in the studies were told that certain (randomly selected) children were smart, those kids performed better, not only in the classroom, but also on standardized IQ tests.Indeed, we get the most out of other people when we believe in them. Research shows that this happens because when we believe in someone,
We treat them better than people we think will fail,
We give them more opportunities to succeed than we give those we think will fail,
We give them more accurate, helpful feedback than we give others, and
We do more teaching because we believe it’s time well spent.
Letting your doubts cloud your belief in someone (or something) practically ensures their failure. Medical professionals call this the “nocebo” effect. Patients who have low expectations for medical procedures or treatments tend to have poorer results than those who expect success, even with regards to well-established treatments. If a doctor uses a treatment with a clinically verified high rate of success but presents it in a negative light, the probability of a negative outcome increases.
Source: Almost everyone who is unhappy with life is unhappy for the same reasons – Quartz