A cynic can be optimistically defined as a person who is dedicated to perceiving the truth, no matter how awful or depressing it is. An optimist can be cynically defined as a person who looks for the kind of truth that makes him or her psychologically most healthy.
With a cynically optimistic definition of truth, we arrive at the cynical optimist -- a person who finds out all the possible ways of looking at the truth, no matter how awful, and then chooses the one which is both plausible and psychologically healthy.