I believe most (or at least: many) users have passwords pretty much standard - they tend to use even literally the same password for most of the systems they access. This is insecure, of course, but the lack of need to remember multiple password, use a software to store them etc. causes it anyway.
Let's just assume the usual password of our John Doe is "johndoe1" - it consists of 8 characters, including a number.
Now, let's say we have a system that makes user choose a "strong" password. The password policy is to include capital leters, numbers and at lease one special character. This makes John modify his password from "johndoe1" to something like "JohnDoe_1" instead.
John does his stuff in the system then leaves, or is logged in automatically every time based on a cookie setting. Any of these scenarios does not require from him to use the password again for a long time. When John gets back to the system, he enters his login and the standard password ("johndoe1"), which of course does not work.
So he needs to reset the password. Some really nasty systems won't allow him using the password he had set before (e.g. Microsoft account, if memory serves), so he needs to come up with another one, which makes the situation even more problematic next time.
Should John be presented a clue about the password complexity at the login page? Would it prevent him form failing on log in process and thus make the whole experience significantly better? Are there any examples of such pattern?