Watch your thoughts, they become words.
Watch your words, they become actions.
Watch your actions, they become habits.
Watch your habits, they become character.
Watch your character, it becomes your destiny.
By - Lao Tse
This quote reminded by someone a while ago. It is clear and straight to the point meaning. We should have mind in our control. Don't assume someone or something too much. Don't play with your mind and of course to get this you have to focus.
Another important thing that I would like to add is to watch our heart. In order to give the best, our heart and our thoughts should be synchronized. Yes, you can go with only one of them, either heart or thoughts. But when it is sync, it will unleash and boost your power and potential.