I run into the same thing all the time... People who forget their passwords all the time or forget them for specific sites that they rarely log into. I always recommend people to use a system that will allow them to retrieve their password when they forget. Whether it be a spreadsheet or a password manager. Of course, the days of spreadsheets are long gone, but I still know people that use it. I am a firm believer in password keepers. Cloud based ones, so you can get your passwords everywhere.
Specifically, I use https://lastpass.com/
So the question is, what do you use and why?