d100 - does it even have to make sense?

I understand that the rolling system is kinda squinky with the d100 - but from what I have seen it goes like this:
Player: I am going to sneak up to the caravan and look at stuff!
DM: Ok, roll it.
Player: Um..okay what do I need to get?
DM: Just roll and we'll see.
Player: Ok, here goes! *rolls percentiles* I got...um...base 47, what do I add to that?
DM: What's your bonus?
Player: looks like a 15%.
DM: ok so it's a better chance.
Player: Does this involve Math?
DM: Deal with it.
Player: Did I pass the sneak check?
DM: Yes, you sneak successfully past the caravan guard and attempt to, uh, look at stuff?
Player: How do I know I made the save?
DM: Oh, ho ho, that's for me to know and you to wonder about.
Player: So I rolled for some vague reason that only you understand?
DM: Yes.
Player: What if we get into a fight? How will I know what's good or bad?
Other Player: Roll low! Low!!!!
DM: Yes, low.
Player: Compared to what? How do I know? Lower than say...50?
DM: Well if it's a 50/50 chance of hitting it.
Player: I'm so confused.
DM: Just the way we like it. Muahar!