Well it's not really a straightforward answer, some say that Don Quixotes outlook on life though slightly comical adds magic, that in reality life is what you make it or how you perceive it. Meaning that if you are happy in life just because others believe you shouldn't be or should have reason not to be, it doesn't mean you need to listen to them and become unhappy just to agree with them. Or even, if you are sad and everyone says you should be happy, it doesn't make it so.

Also you could take that there really is no need to make up artificial monsters in life just because you are bored, even if you truly believe those monsters really exist. Maybe the monster exist more because you need them to, rather then there is any real evidence of their actual existence. In Don Quixotes mind he is a valiant champion and his peasant girl a princess most fair. Others perceive him differently, as a bit of a fool and his love as a tavern whore, which is correct?

Also another interpretation is that maybe you should listen more to the general consensus of what really is or isn't a monster. The trouble is, is that if you continue to believe something is still a monster even if everyone else doesn't see it as such. People will begin to perceive you as slightly crazy or paranoid. It doesn't mean you are not right or wrong or not allowed to believe that something is a monster, it just makes you different and stand out. Fear is normal, fear of harmless things or exaggerated fear of things is perceived as abnormal or as a phobia or paranoia.

I guess it's a pretty mixed bag, but worth a read if only of the synopsis.