fanatic: a person with extreme and uncritical enthusiasm or zeal as in religion, politics, etc.
So far, so good. Although I love music, literature and film - perhaps extremely - I'm able to be critical about each of my three passions.
fan: an enthusiastic devotee or follower [short for FANATIC].
Uh-oh. Mind you, music, literature and film are not included in the dictionary definition for fanatic. But, of course there is that troublesome and vague "etc."; stay tuned re that distinction. And, perhaps you already knew fan was short for fanatic. My recent aha about these two linked words reminded me again how my language shapes my reality, a word to world fit if ever there was one.
A friend tells me he's seen Bruce Springsteen live over 100 times. In Pat's brain out comes the pejorative label "fanatic". Does this friend have an uncritical enthusiasm for Springsteen's music? Impossible for Pat (or anyone) to know. Back when Springsteen's music meant more to me, I saw him live five or six times. Was I a fan? I suppose I was.
Dictionaries can be very humbling tools, don't you think?