Some systems have complex password requirements. Because of this, it may be difficult to remember the password with a particular system. I understand that there may be security reasons for wanting to hide the requirements, but since that information is already available if the user registers, why not make it available on the log-in screen?
Is there any research that indicates it is detrimental to the user experience to provide the password requirements at the log-in screen? Why is this practice not implemented regularly?
I am not suggesting that the requirements always be displayed, but perhaps it may make sense to provide the requirements after a failed log-in, especially if the attempted password doesn't meet the requirements!
For those who want background:
My friend has a website she accesses once a month at most. The password requirements there are strictest I have seen. Every time she uses the site, she inevitably locks herself out and must reset her password. In general, the passwords she attempts do not fit the password restriction rules.