"You may believe that you are responsible for what you do, but not for what you think. The truth is that you are responsible for what you think, because it is only at this level that you can exercise choice. What you do comes from what you think."
In any moment of decision, the best thing you can do is the right thing, the next best thing is the wrong thing, and the worst thing you can do is nothing.
The way I see it is you have two choices in life; you can be grateful for everything life has given you or you can be resentful for everything life has done to you. Your degree of happiness is directly proportional to the conviction of your choice