I've been thinking about this one for a long, long time. And you know what? I can't think of a single "wise" thing a sensei said that wasn't a story told by "the masters."
But I do have one good one that ... um ... made an impact on my training.
I first started karate circa January of 1972. I was a skinny kid who had skipped his last year in high school and had run a year of college cross country. I was burned out on track. It was such a lonely sport, and I was tired of being too damned skinny. So when this Japanese dude from W&M offered a karate class, well I jumped in with both feet.
The first style I studied was Nippon Shorin Ken. My instructor was Hiroshi Hamada, who at the time was just a lowly sandan. He was from the samurai class (technically) and his dad had thrown him in a monastery when he was a kid to straighten him out a bit. He came out as a martial genius, having trained with a who's who of Japanese karate masters of his era. But he still had an "edge."
Studying from him was a love-hate thing. If he liked you, at some point you were going to get the tar beat out of you. Maybe it would just be with a shinai if you were lucky. The worst insult would be for him to ignore you. That would mean he felt you weren't worth his time. It's a strange way to teach, but I value the experience of performing under fear. I do think there was a method to his madness. Outside of class he became a very likable and reasonable person. It was so strange to have him beat the tar out of you in class, and then walk by him outside the gym and see a big smile on his face. But that's how he did things.
After about a year and a half, I ended up taking an extended period of time off. I had a particularly difficult semester in college, and I put school first. Well most of the way through the semester, I got this phone call. It went something like this.
Mr. Glasheen? This is Sensei Hamada. How are you?
I haven't seen you in a while. What's up?
Back in Japan, there was this very promising student. A teacher worked very hard with him and he looked to be talented enough to be a great karateka. One day he just stopped coming to class. Well a month afterwards he was playing pinball in the pinball parlor, and suddenly noticed he was surrounded by his former classmates. And do you know what happened next? They beat the *@%! out of him.
Of course we don't do that in America, but... Would you like to come back to class?
I told him I would. I did come back to class, and participated enough to compete in that year's tournament. When I had my belt test a month later, I forgot one of my kata. I forgot it because basically I hadn't come to class enough. I was failed, and I deserved to fail. I was walking out of the gym with my head down, and my teacher passed me by in his car. "Come back 2 weeks from now, and test again." I did, I remembered my kata, and I passed my belt test.
I can honestly say that if Mr. Hamada hadn't given me that strange phone call about 38 years ago, I might have quit martial arts. But I didn't quit, and the rest is history.