Parents do this:
If the parents are unfriendly, or even abusive, their children will be the same.
If the parents are friendly, their children will be the same also.
Other people do this too, if you are around unfriendly people almost all the time, you'll be unfriendly...
It usually works for any traits (however, it won't work if you've already been made into a certain personality for your young life), so apparently you've been around random people all of your young life, and probably still will be forever.