Optimist" is a word which here refers to a person...who thinks pleasant thoughts about nearly everything. For instance, if an optimist had his left arm chewed off by an alligator, he might say, in a pleasant and hopeful voice, "Well, this isn't too bad. I don't have my arm anymore, but at least nobody will ever ask me if I am right-handed or left-handed", but most of us would say something more along the lines of "Aaaaah! My arm! My arm!