A lot of people change for good. Some people just fall off. Just trying to progress in anything, no matter what you're doing, I feel like any progression you make... some people aren't gonna be around you that were around you.
We are in a survival mentality, and that's hard-wired into our humanity, because we are the winners of an evolutionary struggle of millions and millions and millions of years.
Most of our pocket wisdom is conceived for the use of mediocre people, to discourage them from ambitious attempts, and generally console them in their mediocrity.