Hi Sam,
I think you have had lots of great responses so far, I'll just throw in this little story.
I got my first guitar when I was 14, in 1970. I learned to play by putting my fingers on the strings until I found something that sort of sounded good.
I did this for years and years and eventually got good enough to play with others. I could figure out songs etc. But I had no idea what the chords were called. I couldn't read tabs or notation. I just figured it out as I went along
About 10 years ago I decided to take lessons. It was literally mind blowing. It turns out I was playing a lot of the chords either upside down or backwards. They sounded fine but I was making my life harder than it needed to be. I also thought that, up the neck, all 6 strings had to be fretted in order for the chord to be correct. Nope, depending on the chord you might only need to fret three or four of the strings. What!!!!!!
And for most songs in a culture the chords have pretty common relationships to each other so you can quickly figure out where a song might be going. I literally learned more in 6 months than I learned in all the time before I got a teacher.
So, I think Zen can be a bit like learning the guitar. You can do it on your own, and you can make progress. But a teacher can really help you avoid pitfalls and keep you headed down the right bath. I think the time I spent just banging on the guitar prepared me for the teacher. And I think Zen can be like that too. But mostly I think the teacher you help you guide you down the path they already know.
At least that is what I think today.
Gassho, Shinshi
SaT-LaH