How does it affect our overall life?
First of all you are missing the opportunity to live the experience that life has presented to you. Later on these unlived experiences keep hanging in the mind, waiting to be completed, to be lived. They carry a certain discontentment, which is added to our overall discontentment of life.
Now lets have a look, how it affects our future. I feel most of us would agree that we enjoy anything most, when it is new, fresh, first time. By trying to live our future in present moment, we are indirectly contaminating it, making it familiar and destroying its newness, freshness. Unknowingly we are creating an image of the experience that is expected from future. And when we encounter the future with this image in mind, we either miss the experience because it matches your expectations, so nothing great about it; or we feel disappointed when the experience does not match our expectations.
So what to do?
You will need to use your imagination power to plan your future, your projections well, but don’t over use it. Clearly draw a line where you should stop your imagination. If you note down on paper the goal of the present planning process, it will help tremendously. Whenever you feel you are lost, just come back to the paper and remind yourself whats the goal of this planning process.
One important pointer is that if you put your total energy in planning, you wont be lost in future imaginations. When you are totally into any activity, the very energy of it wont allow you to leave the present moment. Its because of the partial efforts that we get caught in imaginations, because there is some unused energy left that slips into the imagination of future.