“I am an old man and have known a great many troubles, but most of them have never happened.” – Mark Twain
“There is nothing either good or bad but thinking makes it so.” – William Shakespeare, Hamlet
“What you imagine, you create.” – Siddhartha Guatama Buddha
All restatements of one key principle, that our [mental / emotional] experience of the world is an entirely separate thing from the world itself. The latter one has almost no control over, the former one can reach a state of complete control (granted through painstaking and relentless effort.)
Tiger Riding for Beginners 