Excerpt from from The Practicing Mind: Developing Focus and Discipline in Your Life by ~ Thomas M. Sterner:
I have observed my mind many times through listening to my internal dialogue. It goes from one totally unrelated discussion to another. It's reminding me to pay a bill, composing a musical piece, solving a problem, thinking of a sharp-witted comeback I should have made yesterday when someone irritated me, and so forth.
All this is going on while I am taking a shower in the morning. In that moment, my mind is everywhere but where I really am — in the shower. My mind is anticipating circumstances that haven't happened yet and trying to answer questions that haven't even been asked.
We have a name for this: it's called worrying. If you force your mind to stay in the present moment and to stay in the process of what you are doing, I promise you, many of your problems will melt away.
There is a saying: Most of what we worry about never comes to pass.
Thinking about a situation before you are in it only scatters your energy.
"But," you say, "I have a difficult meeting with someone tomorrow, and I want to have my thoughts together before I get into the situation."
Fine, then take half an hour to sit down in a chair and do nothing else but go through the meeting in your mind and be there completely, doing only that. In the calmness of that detached moment, when you are not emotional, think of what you will say, and anticipate the different combinations of responses the person might make. Decide on your responses and see how they feel to you.
Will these responses have the desired effect? Now you are doing nothing else but what you are doing. You are in the present and in the process. You aren't scattering your energy by trying to act out all this in your head while you are eating your lunch or driving to work. This constant inner dialogue, chattering away, brings with it a sense of urgency and impatience because you want to deal with something that hasn't occurred yet. You want to get it done.