you can read the intro, decide it makes sense to you and you therefore understand it, skim the rest, and walk away.
That's just a waste of time! And you are only fooling yourself if you think that you can understand anything that way (you in the general term, I'm not targeting you Trekkin
). No, what I meant by "understanding it's content" definitely includes the boring parts, the math, the theory, the solved examples, the hours thinking "why does the author does it that way" and of course the exercises.
I totally agree with the necessity for an error-checking mechanism (and a reality check too) especially for aspiring professionals. As you have already said a well structured formal education is a lot more than just lectures, it gives the students access to extra resources, it gives them opportunities to gain practical experience, it gives them teachers to guide them. In my experience (biased as it is) I find the actual lectures to be the smallest part of the educational process.
I wonder why they left
As far as I know that species doesn't form permanent nests (they usually disappear during the winter). So each nest was more like a cocoon than a beehive. If you want (and I can find more about them), I'll do a follow up.
edit: It seems that these wasps belong to the wider group of "mud daubers", meaning they make nests (cells) out of mud, into which they then place captured prey and a single wasp egg. Some of the mud daubers will then abandon the nest and the egg and others will stay and protect them. Since all of the cells I found were already open (and empty) I have no way to find which specific kind they belong to.