Sunken cost is an interesting argument (though "fallacy" is an apt description), but I believe it does not address the design mistake made here. Given the compo

Sunken cost is an interesting argument (though "fallacy" is an apt description), but I believe it does not address the design mistake made here. Given the composition of the first UI object (user / pass / submit / register) an user would click "register" thinking that the process is complete, only to gaze in horror as more fields are revealed. If those fields are required from the start (which they really shouldn't be) they should be visible. The 'verbage' is all wrong.