As far as I am concerned I live in all three. I cannot see how anyone can do anything else. The past forms the person we are in the present and while I accept we do not know what the future will bring, we could all die for tomorrow, if we all lived on that basis, we would not commit ourselves to anything; no partnerships, no children, no holidays, no home.
Look at the probabilities, average lifespan is heading for 80, which means while a lot of people do die before that age, many live much longer. So I plan for the future and if the future is not as expected, I change my plans. Simples!