A friend is:

Someone who you can reach out to at a time of distress and they'll be on their way to help you out.

Someone who was with you when you were at your lowest point.

Someone who knows your flaws, yet respects you for the person you truly are. 

 Over the years I have found that it’s harder to keep close friends when you achieve. 

 The close friends to keep will be the ones whose behavior doesn't change when you achieve