I have never broken anything in the field...or anywhere else for that matter! I can't imagine breaking a knife while doing anything remotely normal with it, although I generally don't do any chopping with my knives - I use axes.
Here is what I have done: I dropped an opinel off the side of a boat twenty years ago, when I was a little kid.
I slipped while cutting something in my lap about ten years ago, and gave myself a good cut on the leg.
I stuck an axe in my leg last year while chopping a tree. That was the best one by far. I had been working falling and limbing trees all day with my dad, maybe eight or ten hours of work. I was really getting tired, but I just had the one last tree to fall...
"I don't think I can do it with this axe," I said. It was my little Wetterlings. I was pretty tired.
"Sure you can," said my dad. "Otherwise, my brother will get here, and use his chainsaw."
"Okay," I said. But I was so tired, I didn't bend at the waist. I just chopped from a standing position. I wasn't really focused on it very well, and then I felt a sting. I looked down, and the axe was stuck in my leg.
"Oh," I said. "That will bleed a bit."
"No," said my dad. "Wrong time of year."
"No," I said. "My leg. There's an axe stuck in it."
"Oh!" he said. "Well, I guess that's true, then. I thought you meant the tree. It would have bled a lot of sap in the spring, but not too much now. Too cold."
"Right," I said. "Good call."
So, the point is, I don't worry about breaking stuff other than myself. I worry about hurting myself and losing tools.