Fun anecdote
OK, so this was for Quake, not Doom, but whatevs.
At the time, I was working for a games company, and we had just "headhunted" a new games producer (From Disney).
So after-hours, we are all playing LAN Quake and she wanders up behind me...
Her: "So what's this?"
Me (Giving her the "What rock have you been living under?" look): "Quake"
Her: "So What's the objective?"
Me: "You shoot each other"
Her: "So once you have shot someone once, what's the motivation for shooting them again?"
Me: *Blam* "That was my boss that I just blasted with a shotgun - I could do this all day"