Every band seems to have that one member who's heart doesn't seem to be into things at some point.

Maybe they don't mean to, but that's how they come off sometimes to fans.

What are some examples?

John Lennon of The Beatles!

When the album Help! was released, Lennon started to be cynical with his work. By then he practically abandoned his son Julian and his marriage with Cynthia was almost over. By 1968, Lennon seemed to have lost all grips with The Beatles and when he married Yoko Ono he practically lost it!

Lennon rebounded as a soloist, but it seemed he lost interest with The Beatles by the mid to late 60's.