Adventures Were What They Were Being Protected From

Heinlein always had a hard time coming up with ideas for these boys’ books. He had to invent something adventurous that boys would be interested in, without needing excessive background explanations. And it was always a problem to get the boys out from under the thumbs of their adult “protectors,” because adventures were what they were being protected from. Targeted at a general readership, these boys’ books could not use the genre conventions of the science-fiction magazines — but he could use ordinary science.

Robert A. Heinlein: In Dialogue with His Century, William H. Patterson, Jr.