There are instances when I look back and think of who I used to be.
There are changes in behavior, outlook, goals, thought processes, rationality, preferences, beliefs.
Some events or some people make you go back and think about how things have changed.
However, the people who really make you think are the people who you look up to, admire or detest. By this I don't mean the people who have been your friends for a long time.
I mean the people who have come to know recently and put you on a different plane when you are around them.
One of the most important fallouts is that you tend to assess yourself around people like this and thereby try to make yourself more respectable in your eyes.