The basic fact about human existence is not that it is a tragedy, but that it is a bore. It is not so much a war as an endless standing in line.

This quote is saying that the reality of human life is not that it is filled with tragedy, but rather with boredom. Instead of life being filled with battle and struggle, it is more often filled with tedious everyday tasks, like waiting in line. It implies that daily life is often mundane and tedious, as opposed to dramatic and exciting.