Why should we dwell in the past? We may learn from past lessons, but we cannot change the past. Memories are filled with mixed interpretations,cultural bias or situational values, personal feelings and thoughts. Some might be beneficial to the present; some, harmful; still others, useless, and time wasting....
Why should we dream about the future? The future hasn't come or materialized yet, and our predictions are poor. We might plan our future to some extent, but it would be a mistake to cling on to something that is still in the air, unrealistic, and illusory. We cannot have 100% control of what will happen. Therefore, our future plans has a relative or superficial impact on our life.
Only the present is what we have direct contact with, and have to experience and deal with. It is the present, or the here and now, that is inescapable. It is the reality we actually live in. The Buddha teaches us to focus on the present, try our best to be calm and mindful in the moment when we are capable of breathing in and breathing out. Knowing that we are still alive, and being fully aware of our body movement and thought in the present moment should be the core of our daily practice.