You want a flying car, I want a rocket belt!
But, I am completely sure that an immortal man would be an insane man.
But you would have a flying car, a rocket belt, and, of course, a laser beam. And you’d be mad. Think of the possibilities!
This is why Kilgore Trout is my favorite science fiction author. He never pandered to popular book trends.
An’ I wanna make out with hot, green alien chicks like Cap’n Kirk!
I am completely sure that an immortal man would be an insane man.You, a completely mortal creature, inhabiting a planet in which all creatures -- thinking and non-thinking -- are similarly mortal, declare that you are "completely sure" about the mental state of an immortal creature, one you've never met and can't really conceive of.
I'm completely sure that if biological immortality is ever achieved in humans (and that still won't preclude accidental death or murder, you know), that they will look back on your post here on this server (or the backup server it's been archived to) and smile.
(PS: For the purists reading this, I am aware that there are some single-celled organisms that are considered to be, in a certain sense, immortal.)