The other day, I was watching an experiment on TV where they put some flies in jar with an open lid. Some flies flew out of it, but when they closed it for three hours and opened it again, none of the flies left the jar. They were conditioned to stay in. The same applies to humans, we are programmed to the environment that we live in.
The point is that if the environment is encouraging and growth inducing, we develop and grow, there is no limit. Unfortunately, the opposite is true.