Now hold on, there! It’s not quite as dire as that.
Although my nearly 50-year-old memory of the event is naturally dim (e.g., where did the tools come from?), I’m reasonably sure I did seal the thing properly, because I lived there for a few more years, and there were no leaks. And while I admit to the mis-wiring, now that I think about it, it must have been fixed by the time the house was sold a decade or so later, since no competent inspector could have missed it. And the fan worked.
So I wouldn’t say that the job was in no sense a success.
Did I take risks I may not have been fully cognizant of? Yes. (And that was the main point I was making.)
Did I subject myself, the other residents, and the owner to the risk of improper wiring? Yes. (And that’s the worst part of the story.)
Could a professional have done the job better in every respect? Without doubt.
And this would have been mislearning, as you suggest, if I had gone on to do a lot more improper wiring in other situations. AFAIK (within the limits of my so-called memory) I didn’t.
But I accomplished the task that had been set, and I think that gave me a sense of confidence (admittedly partially undeserved) in my own abilities that let me take on other challenges more successfully. Feeling it is possible to do something yourself, instead of having to rely on others, is an important part of learning new skills.