why not be happy

I really don't understand how we can waist so much of our life, i'm talking about sitting doing nothing. I'm talking about how much of our life we spend mad and frustrated with people, when we could just CHOOSE to be happy. Have you ever had that moment when you realize your living, if you have ever had this experience you know exactly what i'm talking about, if not its hard to REALLY understand what i'm saying. In that moment you realize all those times you got mad you could have CHOOSE to be happy but instead you decide to be mad and frustrated. I've jus been trying to think why would we choose to waist part of our life being mad when we could spend our time happy?