Me: Hey! Why'd you buy cake?
SH: It's from the bargain table. They had just put it out.
Me: But we have cake.
SH: We do? Where?
Me: It's in the freezer. That chocolate cake we got with the groupon.
SH: Oh! I forgot about that.
Me: How can you forget about cake?
SH: I don't know. But I was planning to get a brownie from [the new bakery in our neighborhood] and this was cheaper.
Me: We don't need brownies!
SH: It's cheaper than a beer. In beer units, it's only one half.
Me: Except just because you buy a brownie, it doesn't mean you would buy less beer.
Me: So the point is completely irrelevant.
SH: I was using it as a basis for comparison. It's a small expense.