search engine, which even Yahoo! says is the best Internet search engine, I searched for the exact phrase:
will not devote itself to making you happy
I looked at every hit until I found the paper that noted the source "Man and Superman."
Then I started over and added the word "superman" to the search, and as I recall, I got over 60 some odd hits that all mentioned the source.
In my reply I included links to those hits that seemed most reliable.
Oh, and welcome to the Quotations Page forums.