That is a crucial question. Everyone from philosophers to scientists to inquisitive regular people have wondered about how we manage to understand what we see around us, how we are able to perceive the universe we exist in and are a part of.
One of my personal idols, Richard P. Feynman, physicist extraordinaire, educator supreme, and all around fucking party animal, discusses this central human issue in today's Science Video of the Day.
Richard P. Feynman (1918-1988)received the Nobel Prize in Physics in 1965. Here is a link to his Nobel Lecture, delivered upon acceptance of his well-deserved award. His published lectures are among the most valued physics texts. He had a facility for explaining the most esoteric and obtuse physical concepts in a manner that not only made them understandable but also drew his students interest.
He also wrote some books, very meaningful to myself, that are intended for the general reader, not the heavy physics nerds like myself, and that touch upon much more than just the science he did. They show and describe a way of life and a philosophy that Richard P. Feynman exemplified.
Here are two of them.