I worked for a company that had an online store. When we updated our payment flow, our developer added a small javascript snippet to auto-detect card type from

I worked for a company that had an online store. When we updated our payment flow, our developer added a small javascript snippet to auto-detect card type from card number. Now we didn't need users to choose 'Visa' from the drop-down anymore, we just had fields for 'name on card', 'card number', etc. and then a set of faded-out card issuer icons that would highlight based on which card type you'd typed in. A huge number of purchases started failing because users, confused, would type 'Visa' into the 'Name on card' field instead of their own name, and then wouldn't bother putting their own name into any of the other fields. He ended up changing the HTML to have a drop-down which was completely ignored on the backend just so we wouldn't have failing purchases and a huge support load anymore. In other words, when presented with a card form that didn't ask what type of card it was, people assumed that inputting the card type (which a graphic made very clear was highlighted already) was more important than putting the cardholder name in. We learned a lot of other lessons on that project about not assuming people could ever figure things out on their own.