Why we spend most of our life in a state of unconsciousness

In a sense, the past and the future are both illusions. They do not objectively exist. They only exist in our minds. The past exists as memory or loss. The future as aspiration, hope or despair. To be conscious is to recognise that the present moment is the only objective existence that we can experience. Not being in the present is akin to being unconscious, yet this is how we spend most of our life.

Source

Though thou shouldst be going to live three thousand years, and as many times ten thousand years, still remember that no man loses any other life than this which he now lives, nor lives any other than this which he now loses. The longest and shortest are thus brought to the same. For the present is the same to all, though that which perishes is not the same; and so that which is lost appears to be a mere moment. For a man cannot lose either the past or the future: for what a man has not, how can any one take this from him? These two things then thou must bear in mind; the one, that all things from eternity are of like forms and come round in a circle, and that it makes no difference whether a man shall see the same things during a hundred years or two hundred, or an infinite time; and the second, that the longest liver and he who will die soonest lose just the same. For the present is the only thing of which a man can be deprived, if it is true that this is the only thing which he has, and that a man cannot lose a thing if he has it not. — Marcus Aurelius, Meditations, Book 2, Meditation 14

The full text of Marcus Aurelius’ Meditations is available here.