This is the title of a great little book that I read years ago that explains the way we create our experience of life through our thinking. We think we are responding and reacting to the world around us, but in fact we respond to our thinking about the world as we perceive it.
Two people can experience the same situation entirely differently. I always remember the story of two American soldiers held captive and tortured during the Vietnam war. One saw it as the worst thing that could ever have happened and suffered from his memories of the experience for the rest of his life. The other saw it as an opportunity to go deep inside and learn about himself and human nature. He went on to be very successful in later life.
Exactly the same situation, two different people, two very different responses.
Even when we look at our own responses to the situations we find ourselves in, one minute a new development can feel like a threat, the next like an opportunity. All that changes is our thinking. And it changes without us doing anything!
It's not so much that we should try to control the thoughts that appear in our heads. That never works. The more we resist a particular thought the more we concentrate on it and the more strength we give it. This is the Buddhist definition of suffering, clinging to or pushing away thoughts we like, or don't like. We waste so much time and energy fretting about the thinking that we made up!
Our thoughts don't represent reality, and they arise and change without us doing anything. The trick is to learn to watch this happening. If we do this the noise naturally reduces, our racing thoughts slow down and possibly even stop. The calm, relaxed feeling that emerges is our natural state. It's when we feel most contented. It's when our best ideas come to us. It's always there. We just forget.