Very often, our mind is carried away by a multitude of thought sequences where ruminations of the past are mixed with projections into the future. We are distracted, scattered, confused and, as a result, disconnected from the most immediate and closest reality. We barely perceive what is happening at the moment: the world around us, our sensations, the way our thoughts follow one another, and above all the omnipresent consciousness that our cogitations obscure. A study by psychologists Matthew Killingworth and Daniel Gilbert published in Science showed that 47% of the time people's minds are not paying attention to what they are doing and that these moments of distraction are moments of lesser well-being, hence the title of the scientific article published on this research: "A distracted mind is an unhappy mind." Another study also shows that a distracted mind has less consideration for others. (1)
Our automatisms of thought are thus at the antipodes of attentive presence. This consists in being perfectly awake to everything that arises in and around us, from one moment to the next, to everything we see, hear, feel or think. To this is added an understanding of the nature of what we perceive, free from the distortions caused by our attractions and rejections. For Buddhism, mindfulness must also have an ethical component that allows us to discern whether or not it is beneficial to maintain a particular state of mind and to pursue what we are doing in the present moment. It must be aware of the appropriate antidotes to remedy mental states that cause suffering to oneself and others.
The past is no more, the future has not yet arisen, and the present, paradoxically, is both elusive, since it never stands still, and immutable - as a famous physicist wrote, "the present is the only thing that has no end". (2) Cultivating full awareness of the present moment does not mean ignoring the lessons of the past or making plans for the future, but rather living lucidly the present experience that encompasses them.
You can find out more on this topic in the book The Art Of Meditation by Matthieu Ricard.
(1) - Killingsworth, M. A., & Gilbert, D. T. (2010). A wandering mind is an unhappy mind. Science, 330(6006), 932–932.
(2) - Jazaieri, H., Lee, I. A., McGonigal, K., Jinpa, T., Doty, J. R., Gross, J. J., & Goldin, P. R. (2016). A wandering mind is a less caring mind: Daily experience sampling during compassion meditation training. The Journal of Positive Psychology, 11(1), 37–50.