"Despair" and "complacency" are two diametrically opposite emotions. Literally, what they mean is that being too pessimistic and too optimistic is not a correct attitude towards life, and they can't correctly understand their own values and social connotations, so it is very sad. It is called "two tragedies in life" because people often change from "full of ambition" at the beginning to "full of ambition" later, and will remain depressed all their lives.

It tells us from a philosophical point of view that what seems to be the opposite in content may actually belong to the same point in essence; A thing seems to have changed significantly, but it may not have changed in a sense.