A: Okay, so here's how it works: You step through that door, and you end up back in here, same exact moment you walked in, but with memories of everything you did up to that point.
B: What, like...time travel?
A: Not LIKE time travel. It IS time travel. For some messed up reason, this door in your basement's turned into some kind of interdimensional portal or something.
A: Here, try it -
B: HEY! No way!
A: Why? What's the matter?
B: If I go through that and you're right, how will I know I'm coming back to the same place? What if it just LOOKS a lot like where I was before, but ISN'T?
A: What the heck does it matter then? You'd have no way of telling the difference.
B: How do you know? I've been through it like, ten times!
A: Yeah, but you're not as perceptive as I am.
B: You're - what? I am SO much more perceptive than you.
A: How do you figure?
B: Well, I found the damn thing, didn't I? Freakin door's IN YOUR HOUSE, and you never even bothered to open it!