These is what I heard in a recent episode of Game of Thrones, a famous TV show:

I suppose it's hard for a fanatic to admit a mistake. Isn't that the whole point of being a fanatic? You're always right. Everything is the Lord's will.

This is Merrian-Webster's definition of fanatic:

marked by excessive enthusiasm and often intense uncritical devotion

So, how does being excessively enthusiastic about something imply that the person will be always right about it? Can anyone explain to me how the usage of "fanatic" here is appropriate, if it is? Does it have another lesser-known meaning?