Yeah, I think that line is getting used as a thought terminating cliche. While the statement is certainly true, not being immune is completely ignoring the idea that people can vary in how susceptible they are.

Starting at my feet and working my way up, I flex each muscle as independently as possible and then let it relax. If you don’t manage to fall asleep while focusing on the process, you’re so relaxed by the end that you’re at least really comfortable.