For me the big deal is that if my card doesn't work—my actual plastic card, that is—then it's the retailer's equipment that is faulty. They fumble around with it—using a plastic bag sometimes, or they move to another terminal—and it works eventually. But the issue is almost always on the reader side, not with the card itself.

On the flip side, that retailer has just seen 100 people in a row use their plastic just fine, then you come along with your whiz-bang phone or Coin card or whatever, and start failing. The embarrassment comes from everyone else waiting behind you thinking to themselves, "Why not just use a card like everyone else instead of your complicated technology?" Or, "HEY EVERYBODY! LOOK AT THIS GUY WHO THINKS HE'S TOO GOOD FOR REGULAR CARDS!"

To be clear I don't pooh-pooh these things. I totally understand why people would like to ditch a stack of cards for a phone or Coin replacement. Just explaining why it might be embarrassing to rely on these replacements, and then have them fail.