When things do not go as per your plans
When your expectations are not met 
When you are not where you wanted to be
Tell yourself: 
Everything happens for a reason. You are exactly where you are supposed to be. What's not yours won't ever come to you and what's yours won't ever go away. Everything has a way of working out. In the grand scheme of things, you have no control over anything. This is a big world and forces beyond your comprehension are working towards keeping things in place, making life go as it's meant to be.