Many years ago, I lived the life a student musician playing bass guitar. My teacher placed a large emphasis on jazz and improvisation and after struggling a little with letting go and just allowing myself to play he asked me an unusual question.
"What is the most important note you will ever play?"
I paused for a second and responded without thinking.
"The one I'm playing."
He was a little taken aback.
"I've asked you this before, haven't I?"
I assured him, that he had not. It just made sense to me. This was before I really knew anything about Buddhism so there was no intellectualization over it, I just kind of knew.
So then he asked me another question.
"What's the least important note you'll ever play?"
"The last note I played, of course," I responded.
"I have to have asked you this before... I'm sure."
"Nope. It just makes sense. You can't unplay a note, and if you're all worried about what to play next, you'll freeze up. You can't ride the groove."
None the less, my improv improved. While I understood, I hadn't implemented the idea. I practiced my scales until my fingers knew what to play when, and I improved.
Now I'm not trying to toot my own horn,(bad musical pun, sorry) but I think it's important to stress that we can have realizations on our own, independent of teachings. I'm sure I'd been told several times the very lesson he'd tried to teach me and I just hadn't gotten it before, but the way he asked it that time was my "stone striking a tile" or whatever.
We can read and listen all we want, but until the spot in our mind is in the right shape for the right shaped piece of information, it won't matter. The purpose of our practice is to exercise the mind, to stretch it out and make it more malleable so that it can receive the Truth when it appears. This is the "immovable mind"* that doesn't get stuck by thoughts with preconceived notions.
While I can't really get behind the idea of koan for the sake of koan, I do understand their purpose when used by the right teacher in the right way. I think the classics are difficult since they've been translated so many times they've lost their cultural relevance and they seem to require an encyclopedic knowledge of zen heritage. But I think the right modern teacher would be able to see in their student the shape of that hole in the mind and be able to give them the right shaped piece to fit it. Well, dharma gates are boundless after all.
I've recently come to the conclusion that zen is the ideology that asks me to make the least changes in myself for practice. The changes and means it asks of me also seem to very straightforward and of obvious benefit. I'm not sure if that's the nature of zen, or if it's just me. As I look back over my life, I've noticed other memories, like this one, that were obvious fingers pointing me in the direction of zen.
* I always found "immovable" tricky, but it's not immovable like the immovable object, it's immovable like the unstoppable force. If the mind is immovable, no thought can come and "move" it or make it stray from its path.