Fanaticism is a belief or behavior involving uncritical zeal or an obsessive enthusiasm.
The Fanatics of Tangier by Eugène Delacroix, Minneapolis Institute of Arts
Japanese holdouts persisted on various islands in the Pacific Theatre until at least 1974. Hiroo Onoda offering his military sword on the day of his surrender.
In modern usage, enthusiasm refers to intense enjoyment, interest, or approval expressed by a person. The term is related to playfulness, inventiveness, optimism, zest, verve, and high energy. The word was originally used to refer to a person possessed by God, or someone who exhibited intense piety.
Men reacting enthusiastically
Methodist preachers have been known for their enthusiasm in promulgating the doctrines of the new birth and entire sanctification to the public at events such as tent revivals and camp meetings, which they believe is the reason that God raised them up into existence.