When people show you who they are the first time believe them. Not the 29th time. When a man doesn't call you back the first time, when you are mistreated the first time, when someone shows you lack of integrity or dishonesty the first time, know that this will be followed many many other times, that will some point in life come back to haunt or hurt you.
Live your life in truth. Don't pretend to be someone you're not. You will survive anything if you live your life from the point of view of truth.