Well it could be your own secret hashing or concatenation algorithm which you can do in your head. For example, you could use parts of the domain name to map to

Well it could be your own secret hashing or concatenation algorithm which you can do in your head. For example, you could use parts of the domain name to map to a specific word from a list that you've memorized. But there is an infinite number of rules you can choose from so you don't lose any security.