The world breaks everyone, and afterward, some are strong at the broken places. If you cannot do great things, do small things in a great way. Great achievement is usually born of great sacrifice, and is never the result of selfishness.
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.
You have to have the service mentality in the sense that you subjugate your own ego, and you subjugate a large part of your own life to really helping other people, being successful on their behalf.