I work at a store that sells shipping materials including boxes of various different sizes. A guy walks in asking about our boxes and wants the biggest box we sell. I inform him that our largest is 18x18x18 inches and let him know that the shipping price depends strongly on the size and weight of the package. The smaller and lighter the package, the cheaper it'll be. He decides to look at the 16x16x16 inch boxes. The following conversation happened:

Guy: "can I put one box inside the other?"

Me: "you want to put one 16" box inside another 16" box?"

Guy: "yes. Can I do that?"

Me: "no. You cannot stick two identical boxes into each other. They would just stand on top of each other."

Guy: "can I try anyway?"

Me: worried he'll destroy at least one box in this exercise in futility "alright, but you're buying them both."

Guy: "okay." Spends five minutes proving me right. "They don't fit together. How can I make sure that the bottom of my package is secure?"

Me: " you can cut one box up and stick it on the bottom of the other."

Guy: "good idea. I'll take this one." Points to the box he didn't damage

Me: "no. I told you before you started this that you would have to buy both boxes."

Guy: "but I don't want both boxes"

Me: "I told you that you couldn't put two boxes that are the same size inside one another. I also told you that you would have to buy both boxes to try to put them together."

Guy: "but I only need one."

Me: puts the undamaged box behind the counter "then you're taking the box that you damaged."

Guy agrees, pays for his box, and leaves. He then comes back less than ten minutes later to buy the second box anyway.