It took me three years to realize I should be ordering the special rolls when I got all-you-can-eat sushi.

At first, I reasoned that the other sushi was free, and paying infinity times as much for a slightly better piece of sushi couldn’t be worth it. In a sense, this was correct – for any non-zero number, you would want to avoid multiplying by infinity. The first few times I went, I thought through the decision. I had proof that I was willing to pay $0 for the normal rolls. Given that, was it worth it to spend money to get slightly better sushi? I felt like it wasn’t. Free was a compelling price point, and spending money to get a special roll felt like a waste.

But the special rolls at my local sushi joint cost $1. And they were definitely much better than most of the other rolls. One had mango, one used jalapeno to great success, and one was baked and covered in scallops and delicious flaky bits. (Though they weren’t all hits. One had a very smelly mushroom topping that caused my tablemates to literally gag.)

One day, looking at the menu, I realized the correct question to ask. Not “do I want to spend money right now?”, but “would I be willing to spend $1 more to get the special rolls at other restaurants?”. Once I framed the question like that, the answer was clear: at most other restaurants, I would rather pay $10 for a special roll than $9 for a regular roll. The marginal cost, not the percentage difference, is what matters.

Once I made this decision, I split my choices among the regular and special rolls. Not only did those rolls taste better, but having a wider variety made eating all I could much more enjoyable.