Well...I worried about that a lot too, since a lot of people were saying that's just how this place works, and that's not really an answer. Th-That's just believing something because you want it to be true, since you can't really prove it.

[He's still not really on board with that, but luckily he did get a better answer, at least specific to Greg.]

People don't always show up at the same time here though? O-Or from the same time, is what I mean. We have a friend, Beatrice, and from me and Greg's perspective, she's a few days in our future. It's not much but...she'd been travelling with us. So...i-it's kind of complicated, but if Greg didn't go back to the point we came from, Beatrice would remember him going missing. But, since she said we were there the whole time, we must go back at some point, to close up the loophole.

[He makes a vague circular gesture with two fingers, to suggest "closing the loop"...but then he realizes it might not have been explained to Dipper at all, so he quickly adds:]

That happens to everyone here. Apparently time stops for us and starts up again when we get sent back? I-It's kind of like pressing pause on a cassette player. And then we don't remember when we go back, so...no one knows we're even gone.