Comment by PaulHoule

This was a 1970s paperback by someone who attracted attention for his work on spiritual matters and sold a lot of books but didn't leave an organization behind so you can find his books at used bookstores.

https://www.amazon.com/Discovering-Secrets-Happiness-Intimat...

Not rare at all but some people might say it has some prurient interest (talks about his sexual misadjustment) so maybe they think it has to be limited access or maybe people will steal it or something. (The same library kept Steal this book in a restricted area of the stacks but let me check it out.)