You bought three sizes of the same shirt knowing you would keep one.
You did not feel bad about it. You did not even think about it. That is the whole point.
Amazon shipped you all three, for free, and will take two of them back, for free, with no box and no tape and no printer, at a drop off point four minutes from your house.
Now count what that costs. Outbound shipping on three items. Picking and packing on three items. Return shipping on two. Receiving, inspecting, restocking or disposing of two. Customer service if anything goes wrong. And the refund itself, which erases the revenue entirely.
Amazon paid for a round trip and ended up with two used shirts and no money.
Gif by GrandVision on Giphy
That is not a rounding error. Returns cost the retail industry an enormous amount, and apparel is the worst category there is.
And yet Amazon keeps making returns easier, not harder. Every year, fewer steps. No box. No label. Just walk in and hand it over.
A company does not spend years reducing friction on the thing that costs it money unless the thing is doing something more valuable than it costs.
Here is what it is doing.