All evidence shows that it has little to do with education, background, circumstance or even intelligence. The one common trait of successful people is the expectation that success is possible and turning that expectation into daily action.
In my work as an international business trainer, I have noticed that people who “expect” to be successful and happy usually are. Those who believe their success and happiness depends on luck, circumstance, or other people, usually are not.
This law of expectation has been proven in studies. In one experiment, teachers (chosen at random) were told that because they were the best teachers (they weren’t), their students (also chosen at random) had extremely high IQ’s (they didn't).
The teachers were instructed not to treat them differently. However, those students out-performed their district peers in all areas of scholastic achievement. The only difference was the expectation the teacher had of the students.