Nine years ago, when I was at the height of my heavyweight walking days, I went hiking with my wife and her sister in the remote mountains of the Iide Range in northern Japan. I was using a Dana Designs Terraplane and carrying two tents because I hadn't had the time to check to see if the bigger tent was big enough for all three of us. My pack weighed 25 kg (55 lbs) and I wasn't exactly in the best of shape. Since it was my wife's sister's first time to go hiking I ended up carrying some of her stuff, too. And not taking the time to read the literature (in Japanese) about the Iide Range I had no idea that it was some of the toughest climbing in Japan (lots of razorback ridges, one where we literally had to straddle the ridge for about a hundred meters). Really, really, really stupid, especially since I had already had many years of backpacking experience.
On the third day, exhausted and tense from having to make extra sure my wife's sister was okay, I stormed out of a mountain hut after sheltering from strong winds and rain for a snack break. My pack was so heavy that I couldn't keep my balance properly. Just down the slope my boot caught on a creeping pine root (creeping pine are coniferous bushes that live above treeline in Japan) and I tripped, sailed over the edge of the cliff to my right, landed on a ledge just below, and hit my head on a rock. My wife saw me and ran back to the hut in a frenzy. Luckily there was an experienced mountain climber there who'd been walking with us for half the morning (he'd climbed Annapurna and recently Acongagua) and he quickly pulled me back to safety and bound up my head. Seems I was fine, physically. No concussion. But the experience completely shook me up. Talking to that mountain climber and later consulting with myself, I vowed never to go so heavy again or to get lax and be so unprepared.
Needless-to-say, my wife's sister didn't talk to me again for years after that. Can't say I blame her at all. Not only did I exhibit stupidity as a mountain walker, but as a leader as well. You live and learn.
Tomorrow I will be going on a six day jaunt over the Kurobe Range in the North Alps here in Japan. The walk is similar to the Iide Range walk, but longer and more remote. My pack is now 11 kg (including food and water) and I still consider it too heavy (I have a lot to learn about lightening up with the food, but having insulin dependent diabetes makes it just too scary to cut it too close. I've had scary experiences with that, too, but that is another story).
I guess the lesson is that reading about what you need to prepare is just not enough. You really have to get out there and learn from your mistakes, because mistakes you will make.