Ruark and TANSTAAFL

Ruark's use of the phrase antedates Heinlein's use of it. It shows up in chapter 9 of The Old Man's Boy Grows Older:

The thing most nonhunters don't realize about the artistic pain that goes into filling four ounces of flesh-and-feathers or seven tons of elephant with the correct prescription is that when you walk out thataway you got walk back thisaway. Non-fishermen don't realize that the current is likely to run steadily in one direction, and if you float downstream, eventually you have to fight your way upstream. From rabbit to tiger, from bobwhite to buffalo, from sand perch to marlin, there's no such thing as a free lunch.

Now, I'm not saying that Ruark was the first one to use the phrase. According to Wikipedia, it has been in use long before Ruark or Heinlein. My theory, though, is that Heinlein, who was a contemporary of Ruark's, may have seen the phrase in Ruark's book or in the pages of Field and Stream. Since Ruark's use of it came in the early 1960's, it may have inspired Heinlein to use it in The Moon Is a Harsh Mistress, which was being written at roughly the same time.

Just my opinion.