But he compares it with a man trying to swim across a river that has a very strong current. If that man wants to land at a particular spot on the other side, he needs to aim at a spot much further upstream. Only by aiming much further upstream does he least have a chance of reaching his spot.
Note that it also would not suffice to chose “pretend” that you’re aiming for the point further upstream. You actually do have to swim in that direction with all you’ve got. Otherwise you are going to be landing far downstream from where you intended to.
I think that Heinlein quote here is trying to do the same thing.
To me the quote also meant that knowing disparate things could lead to useful knowledge to the individual, even if they didn’t think so before.
A programmer learning how to fix an engine, despite not being interested in cars, may give them insights into how systems work that can be applied in their programming work
For the most part I've always known, or at least thought Ive known, Why I'm Miserable, and the only skills that have a part in it are math and driving a car, and a few highly specialist things I wish I'd learned, like going into industrial controls.
I do know people who are uncomfortable being a specialist that couldn't function without industrial society as we know it, but the quote seems to paint it as a universal thing.
Everyone should probably have more skills than they do now, including some that aren't currently needed for most people, but I don't want to throw away specialization entirely, or nobody will be able to build satellites and cell phones, and people really will need to set bones without medical aid.
Some things are just really far outside of what a person expects to need, and everyone should probably pick a few of those, but I'm perfectly happy not knowing how a parser generator works or how to use a lathe I don't have space for. There's just too many skills to learn them all.
Then again, a rare few seem to be able to make real progress in a specialist field while also knowing a bunch of awesome skills and doing ninjutsu, but most people say "Yeah, that's why I have a job, to pay people to do that" sometimes and are fine with it.
But I go to events and do physical repair work, if I had to sit in an office of just all code all the time, maybe I'd have extreme views too, I've met a few people who were almost sad to watch, because they didn't seem to exist outside of code.