" ... The surest means of disarming an anger or lust was to turn your attention from the girl or the insult and start examining the passion itself. The surest way of spoiling a pleasure was to start examining your satisfaction. "
— C. S. Lewis, Surprised by Joy
Introspection, as Lewis goes on to point out, is actually rather misleading. The very act of turning our attention from a beautiful thing to the experience of beauty itself promptly causes that experience to stop; and we are led to believe that "beauty" itself consists in no more than remembered words, images, childhood memories, or associations with emotion. Thinking about the thing is never identical with the thing itself.
As above, he frames this by-the-bye as a bit of advice: that you can make your own experience of emotions more "rational" (i.e., less strong, less unruly) by taking better care to examine them. And it would be awfully useful if this were unreservedly true.
the Experience of Inertia
But this technique is not absolutely perfect — at best, it is only mostly reliable. The truth is that our minds are far more entangled with our bodies than we are quick to suppose.
Experience itself tells us that our emotions may not so easily killed as all that. They can have a life of their own, continuing on without the support of our thoughts and even against our mightiest efforts to subdue them by mental discipline.
Closet Platonists
We forget this — possibly because we are, by default, "closet Platonists". We unconsciously make sharp distinctions between "myself" and "my body" — "it's my body and I'll do what I want with it", etc. etc. etc. We find ourselves suggesting that, after all, morality is a thing entirely "spiritual" (whatever that means) and so can have no influence on what we happen to like doing with our bodies (which are, after all, something quite different).
We see this vague bias at work in various scientific theories, too. Often some eminent biologist, or more likely some enthusiastic hobbyist, will hold up some study on brain chemistry to prove that, after all, thoughts are only chemicals, or electrical potentials, or what you will. They will claim that all human thoughts are entirely determined by brain structure; and that, if only you could put a man down inside a X-ray CT machine, you could read his thoughts like a book.
By a curious mental accident, they always seem to leave themselves out of their own system; they may describe everyone else all right, but their own system cannot explain how they themselves arrive at their conclusions, nor give any assurance that their conclusions are necessarily true. (For if thoughts are only chemicals mixing or charges accumulating, if all our concepts of "truth" or "beauty" or "goodness" are purely fictitious and might very easily have been other — then our thoughts can have no meaning.)
Anyway: we quickly find that we are not so neat a division between "mind" and "body" as we are quick to suppose. We are not completely "mind", remaining — like Queen Victoria — unamused because unaffected. But neither are we chemical automata, completely dependent on our surroundings.
Instead, we are some sort of messy combination of both.
Messy Brains
We have a daily experience of our minds as minds: thinking, judging, analyzing. We reason logically and validly. We discover truth and uncover falsehood. We recognize beauty when it appears to us. We not only know, but know that we know. We not only experience time, but stand sufficiently outside time to see it flow past.
Yet we are embodied — physically, carnally, dirtily. We are held hostage to our senses. Our thoughts are driven in tumult before sudden storms of emotion. Spells of irritation or stress can render our powers of judgement and discernment helpless. We are really quite inconveniently messy.
Reflect, again, on the first test of all metaphysics everywhere: "does it meet the test of our experience?" To put it in other words, our philosphizing must be about fact, not about theory. We reason from what the world really is, not from what we should happen to think most rational or agreeable or comforting. This is yet another reason why Philosophy will always be a valid pursuit — why it will always remain a Science in its own right.