My favorite example annecdote: when signing up to pay for Dropbox, I got pretty far along the tunnel. I think after giving Credit Card details, but I'm not sure

My favorite example annecdote: when signing up to pay for Dropbox, I got pretty far along the tunnel. I think after giving Credit Card details, but I'm not sure. At that point, I was presented with a choice: "Pay monthly ($10 per month)" or "Pay Yearly ($8 per month, paid in advance". Being faced with this question, I decided to think about it, then left the page and didn't sign up. I did end up signing up a while later, so maybe this doesn't mean anything, but I could definitely imagine not remembering and ending up never signing up. And all they had to do to was add another option: "Sign up for monthly billing ($10) per month. Don't worry, you can later convert to a year and start saving from that point".