That's a very bad recommendation. Very few people are capable of remembering unique 10-character passwords for each site. I have like 100 passwords and accounts for various systems and I'm certainly not able to remember each of them. So either I start reusing passwords or I use a password manager.
For work and home I have nearly 500. The GP recommendation is absolutely terrible advice.
You can vary the password based on the domain name with a predictable algorithm that only you know.