Leading a human life is a full-time occupation, to which everyone devotes decades of intense concern. - Thomas Nagel

Consciousness is what makes the mind–body problem really intractable.

I am not adverting here to the alleged privacy of experience to its possessor. The point of view in question is not one accessible only to a single individual. Rather it is a type. It is often possible to take up a point of view other than one's own, so the comprehension of such facts is not limited to one's own case. There is a sense in which phenomenological facts are perfectly objective: one person can know or say of another what the quality of the other's experience is. They are subjective, however, in the sense that even this objective ascription of experience is possible only for someone sufficiently similar to the object of ascription to be able to adopt his point of view — to understand the ascription in the first person as well as in the third, so to speak. The more different from oneself the other experiencer is, the less success one can expect with this enterprise.

[W]hen the objective gaze is turned on human beings and other experiencing creatures, who are undeniably parts of the world, it can reveal only what they are like in themselves. And if the way things are for these subjects is not part of the way things are in themselves, an objective account, whatever it shows, will omit something. So reality is not just objective reality, and the pursuit of objectivity is not an equally effective method of reaching the truth about everything.