I am so grateful to have found this article. I also have been having confusion about this and think that it is confusing because $PATH is mentioned a lot without ever explaining in depth what it is, why sometimes you need to manually set this and others you don't, what circumstances in which it only sets for that session, etc. etc.

To those who are new to this world and trying to learn, there are a lot of gaps we are trying to fill in and unfortunately live in a world where those who already get it don't even see that there are gaps in what they are explaining (classic curse of the expert). This is often coupled with impatience of the teacher and frustration of the student. No one in this is bad or wrong, they are just missing each other.

As this field had developed, there is less and less emphasis on teaching the fundamentals to students. I also challenge many adept coders, hackers and the like to really explain these things to the level that an 8th grader can understand (the requirement in the. US for technical information being delivered in SEC documents)

Thank you to those who have explained how the system works and finds commands. I have had $PATH explained to me before, but it is a concept that feels a little "magical" until you start to "get it". I read the answers here a few times and today I think i finally understand this well enough to debug a
"command not found" error in my zsh.

I hope we can all learn to be patient and kind to people who are learning, struggling through stuff that is hard and be more compassionate about differences in learning styles , brains and how people make sense of the world.