"It's a great magic amulet.""Certainly is."
"It's exactly what I need to clear that one level."
"And you have the gold to afford it."
"I know. I just can't carry it."
"...it weighs three ounces."
"But it takes up a three by two space."
"...what?"
"Now my armor, that's six by four. And for some reason, I can't put the amulet directly over it and clearly I can't exactly go into that level without armor, right? Also, I'm carrying twelve potions, eight scrolls, and four meals in case I get hungry, and those take up as much space as another suit of armor. So maybe if I use some of those in a hurry... but then I can't come back here and grab the amulet, not until I clear the level."
"I don't understand what you're --"
"Wait! There's the money I have to give you for it! -- no, that won't work. I can carry an infinite amount of gold in a single one by one space. Gold stacks. No matter how much I give you, the rest still takes up only one space. Now I could pay you in jewels because each is a one by one all by itself, but for some reason, even though they're the most precious item around, no one takes them as currency. Weird, right?"
"That should only be the least weird thing in this conversation. And if you have infinite gold, I'm increasing all my prices more than the amount I normally would just to cover having to listen to this."
"It's my fault, really. I never should have take a pike as my weapon of course."
"Knowing in advance that I'm going to regret this -- why?"
http://tvtropes.org/pmwiki/pmwiki.php/Main/GridInventory
"I'm only allowed to store pikes on the diagonal."