It's easy to see the overview as a set of adventures, leaving Earth and going to other planets, getting promoted, but it all has one goal: getting to that position where Max's freak talent is the only thing that can save them, where he becomes captain and astrogates them home. Everything leads to that. It's climactic. You couldn't predict that is where it would end up (I think, I don't know, I first read this when I was twelve), but there aren't any false leads. And beyond that, the real story is Max learning lessons--from Sam, from Eldreth, from his experiences--and ending up back on that hillside with a job to go to. Both stories end up at the same point, and everything reinforces the theme not just of Max growing up but of him learning what it is to grow up and what he actually values. At the beginning he's a kid with a freak talent, at the end he's a man who has lied, told the truth, seen a friend die and brought his ship home. There are no false moves, everything goes towards that. And it's a great end. All his juveniles have great ends.Starman Jones, or how Robert A. Heinlein did plot on a good day
Now Heinlein, from what he said about how he worked, did all that entirely on instinct, sitting down and writing one word after another and doing what happens and where it's going purely by gut-feel. When he gave Eldreth the spider-monkey, he wasn't thinking "and later, it can rescue them from aliens" because he had no idea at that point that they'd get lost and end up on an alien planet. But when they got to the alien planet, he knew what he had and what he wanted to do because of the way it flowed. But it works like wyrd, where the beginning is wide open and it narrows in and in so that at the end there's only one place for it to go.