Many people consider the idea trite that you are in complete control of your thoughts and your happiness is 100% up to you.
The truth is that there is nothing around us that is as controllable as our thoughts, and what goes on in our heads is truly free, that is for the time being.
One of the keys to happiness is as you grow old, to find those things that free your mind and re-center it. This may be exercise, writing, artistic endeavors, but finding that lever to freedom is a great gift and one that you owe to yourself.

Hugh Mcleod