An old college buddy asked, "If the present is so charming, why does my mind wander away from the present?"
I guess the assumption here is that experiencing the present moment is more charming that reminiscing about that perfect day at the beach near Puerto Vallarta last year or day dreaming about scuba diving in Aruba next year. This reminiscing and day dreaming can also be quite charming! But, I think what my friend is getting at is very interesting and a great question. It depends on the depth to which we experience the present.
The practice of Chan emphasizes living fully in the present moment as does mindfulness practice of the Theravada tradition. If we are to become fully awakened to life just as it really is, it necessarily is in the present that this awakening will occur. During meditation, as the mind becomes more focused or unified it becomes less bound by thoughts. As fewer and fewer thoughts arise, the mind naturally becomes clearer, brighter, lighter and more expansive. This experience can be blissful or simply deeply contenting. During activity, this cultivation or habituation of a more unified mind naturally is more content to experience what is at hand. If the mind is clear, focused and content, there is less likelihood that it will be distracted by mundane thoughts that might arise. The practice of mindfulness actively builds on the clarity gained through meditation and consciously cultivates moment-to-moment clarity of whatever is arising and passing away from conscious experience. This can also lead to a mind that is clear, luminous, settled, and deeply satisfied to just be in the present, moment after moment. It is from this settled state that perception can refine and things can be seen just as they actually are. It is from this perception that insight into the fundamental truths of life occurs, which we know from Buddhist suttras and the writings of past masters can be a very liberating experience. Chan practice can lead to experiencing such charm in the present moment that there is no arising of craving or aversion. The need to reminisce or day dream evaporates when one can simply experiencing the present moment with sufficient clarity.
In that case, the answer to the question is until the mind is sufficiently cultivated and refined, the contentment experienced in the present is not charming enough to keep the mind focused, expanded, and aware in the present.
On the other hand, even advanced practitioners think of the past or future as the need arises. And even when the need doesn't arise, it's the nature of the mind to think thoughts. What is qualitatively different is that thoughts that arise are simply thoughts and the mind doesn't attach to them. They arise like a bubble as a child blows through the hoop. The thought expands from nothing but some slight impulse, takes shape, and floats away. A settled mind is aware of this arising and passing away of feelings, thoughts, and perceptions. The more awake and settled the mind, the finer the awareness of not only mental phenomena but also all phenomena rising and passing away in the environment. This awareness of the arising and passing away of mental and physical phenomena leads to the direct experience of a most fundamental nature, the insight into impermanence. The entire universe is seen as a massive flux of interrelated or conditioned arising of phenomena, and the dissolution of the same when conditions no longer support continuity. It may appear that the entire world is undergoing massive oxidization, as if everything is undergoing a catastrophic chemical reaction, burning, and be an awesome experience. Or, it can be like a symphony of such perfectly interrelated harmonies that the mind is arrested by the absolute perfection of it. However the realization of impermanence occurs, it is not an intellectual reasoning, but a direct and complete perception that leads to life changing insight. This insight can lead to further insight into the nature of the self.
Until or mind is sufficiently cultivated, the mind is like a monkey that is always chasing desires and averting fears. Once the mind is cultivated, it response to the environment, situations, and people with wisdom and compassion. A satisfied mind naturally has compassion for others that are suffering and a clear mind has the wisdom to know how to help them. The satisfied mind is a product of silence and a clear mind is the product of illumination. The Chan practice of Silent Illumination is extremely beneficial in cultivating a content, clear mind. The mind still reacts to things in the environment. When a bus is coming one gets out of the way. And one still makes plans for the future and reflects on what went wrong to do better next time. But, the predominant mode is to be aware of things as they occur and react in a way that is appropriate to the need of the time.
An undisciplined mind will not stop with an initial thought. It won't be aware of the thought arising and passing away. The mind attaches to the thought and becomes lost in a succession of subsequent thoughts. We long for something in the past or fear its reoccurrence, or regret what was done or said. Or we hope for something in the future or worry that it may happen. We are conditioned from beginningless time to crave for more and dread what we don't want. But, when the mind is settled enough, there is greater and greater contentment and though a thought may arise, it is acknowledged and just passes away if nothing more is required. The mind returns to a state of contentment that is simply aware with a clear, bright awareness. But, it's our habitual outward oriented craving and aversion that obscures what would otherwise be quite a contented state.
It is interesting to note that a person can experience unified mind, pure, unobstructed awareness, impermanence, or self-nature and then regress back to being overshadowed by mundane thoughts and day-to-day situations. What we are up against is a very powerfully ingrained habit cultured from beginningless time. That's why we need a practice like Zen to lift the veil and open our eyes. Then we need to refine the practice and cultivate seeing things just as they are without the imaginary ego or self getting in the way to distort the picture. If we get the self out of the picture, the whole thing opens up and everything converses with every other thing, infinitely correlated and perfectly functioning. It's all perfect when we get out of the way.