Although the fact that our phenomenal experience is "composed" of qualia should be evident from infancy, it is actually difficult to become aware of the full richness of the qualia dimension.
Myself, I did not become aware of the problem of qualia until the age of 31. On that fatal night, February 1994, I was returning home from the Institute of Physical and Chemical Research (RIKEN), where I was conducting my postdoctoral research. I was on a train. I was writing ideas, diagrams, and equations into my notebook, as was my custom at that time. That particular night was rather "productive", at least in quantity. I remember that I made about 10 pages of entry.
I was standing at the edge of a car, where two carriages are connected by the coupler bridge and rubber covers. As you know, this part of the train is particularly susceptible to the noise that the train cars make as they go along the railway.
While making notes in a hectic speed, I must have been listening to the train noise: clickety-clack, clickety-clack, clickety-clack. There was nothing unusual in that situation. I did not have any premonition at all what was to come. What did come, it turned out, actually changed my life beyond recognition.
All of a sudden, I realized that the sound that was reaching my consciousness was composed of vivid qualities. Clickety-clack, clickety-clack clickety-clack. Qualities that cannot be fully described by words. Just this immediate impression of sensory qualities. It should be an evident fact for anybody. Even a child knows that a train goes clickety-clack. However, until that moment, I did not realize the very serious nature of the problem presented by the fact that our conscious sensory perception has the qualitative dimension.
I was trained as a physicist. I got my Ph.D. in the physics department of the University of Tokyo. As a physicist, I knew for a fact that the objective behavior of everything in the universe apparently obeys in a precise manner the laws of physics. As a physicist is wont to say, if you know the "Hamiltonian" of the universe, everything should be describable in terms of a set of equations.
I held that belief at that time, and actually continue to hold that belief to this day. Until that fateful night on the train, I did not have any idea that there should be something "external" to the physical description of the universe.