The biggest obstacle to a peaceful inner life is entitlement. Why? Because the biggest reason you get angry is when someone takes away something you think you have a right to. The more you think you're entitled to, the more angry you will get. If you think you "deserve" health or wealth or a beautiful spouse or whatever and don't get it, you will be angry.

But if you're grateful for what you do have and don't take them for granted, you will be much more positive and less angry.

Simple to understand, hard to practice.