You are shopping on Amazon. You add something to your cart, and you decide to checkout. Amazon asks you for your account information. "Enter your e-mail address," it says. You do. Underneath that are two radio buttons. One says "I am a new customer." The other says "I am a returning customer," and offers a field for your password. You click, or tab, to the next field and enter your password. You hit enter, or click the sign in button — it makes no difference to Amazon because this is what it replies:
You clicked on the button indicating you're a new customer, but you also provided a password. If you're a new customer, please do not enter a password yet (we'll ask you to create one later). If you're a returning customer, please click on the button indicating that you already have a password, then type in your password.
You are confused and dismayed. You did NOT click on the button indicating you are a new customer! (What button?! The only button in the page says "Sign in!") You realize the default on this login page is set to "new customer." You wonder why it does not understand your intentions. It could see that you have entered a password, yet it did not bother to query the database; or, why did it not simply toggle the radio button as you tabbed or clicked into the password field?
You get the feeling Amazon holds some kind of institutional animosity towards you, like being sent to the back of the line at the DMV because you made a slight error on one of their forms.
But you forget about this, until the next time, and the time after that...