Heinlein's quote I think is not to be taken too literally. It's the notion that human beings can do so many things and there's a lot of synergy in knowing that many things. You'll start seeing connections between one and the other and solve problems in activity A while doing activity B. It's fun too!
I might not know how to butcher a pig, but I know multiple programming languages, multiple human languages, I ski, I climb, I skate, I ride bikes. I can cook foods from cuisines from all over the world. I read books on things I haven't formally studied.
Life is just more interesting if you're not a one trick insect.
Sure, but it doesn't help you actually decide where the line is between "things which I should focus on learning" and "things which are massive skills that it would take many years to learn and I shouldn't bother." My biggest problem here is with "learn how to plan an invasion".
I might not know how to butcher a pig, but I know multiple programming languages, multiple human languages, I ski, I climb, I skate, I ride bikes. I can cook foods from cuisines from all over the world. I read books on things I haven't formally studied.
Life is just more interesting if you're not a one trick insect.