It doesn’t say to master all those things...in fact that’s the opposite of his point, which is to be reasonably competent at a lot of things rather than being helpless without a specialist around. Heinlein’s characters are (sometimes hilariously) self-sufficient, but respectful of true expertise.

My perspective has been to be able to "speak the language". You may not be able to rebuild your engine, perform surgery, build your own PC, etc. But know enough that you can have a meaningful conversation with the experts.