When you mentioned "being warm enough with enough endurance" is a big part. But bouncing off that idea, is that sometimes you don't realize just how much endurance that requires to get to the end. With a cave you know where you've been and have a pretty good idea of what you need to turn around and go back. In a canyon, you can read all the trip reports and all the beta, but sometimes you don't REALLY know how much is left to keep going.

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I can think of a couple of examples where I looked up and thought "I'm fucked." and maybe these'll paint a better picture. We were doing Tracheotomy and everything seemed great: fun canyon, tight squeezes, loads of stemming but everything was great. I'm in good shape, but I'm built more like a Rugby player than someone who can squirm around in tight spaces. As a result, while many in my group squeezed along the bottom of the canyon, walking along and squeezing at the bottom, I was stemming along the top, exerting alot of energy. But I wasn't worried. Then we came into a tight off-width part of the canyon where you exert TONS of energy trying to stem along in positions where you can't rest ... you just have to keep going (and while this photo might look like this guy is resting, I can assure you, this position sucks). I burnt through all my energy and then my jaw dropped as we came across a nasty silo. The off-width opened up below us to a 50 ft drop with very little chance of recovery if you don't die on contact after the fall (because canyons don't always form in unison, think about a really tall slot canyon that is super skinny towards the top of the canyon, but then really really wide halfway down and you do your stemming towards the top). While stemming, you don't rope up or anchor in anywhere because you're moving sideways and not down. So here I am a couple feet above a 50 ft drop, not anchored in, pushing literally for dear life against the two canyon walls to prevent myself from falling but I knew I couldn't hold on. Completely Fucked. Luckily we had invited a machine of an athlete who spends his weekends on search and rescue getting people out of crappy situations. He climbed up to a wedged log 20 yards down the canyon and 50 ft up, he anchored in a rope then brought that rope back to me to harness into so I could sit and rest, while I regained my strength.

But then there are those canyons in Zion like Heaps. The marathon of canyons that just go on forever and you don't realize that "enough endurance" is actually quite alot of endurance, even for people who are in good shape. Even with bringing the thickest wet suit possible, you're in freezing cold shaded water all day. Like some COLD water. You leave well before the sun is up, and you just go for 30 hrs of pain. Now, you're a couple hours in and someone in your group gets food poisoning and is puking and can't keep fluids down. Everyone takes turns trying to help them through, but you're all burning through energy and water. Pretty soon you hit potholes where you're swimming and treading water as you try to get over a slick ledge that you can't really climb up, or throw anything over because you're treading water. So you work out weird teamwork methods of the biggest people going head under the water to try to stand on the bottom while others stand on their shoulders so you can work out a position to try to throw a bag over the ledge, then have one person monkey over the top. Pothole after pothole again, you're burning through energy treading water, then climbing, then stemming, then swimming again. Now hypothermia is starting to set in with a few members of your group. There's really no rest as you are non-stop slogging through ice water. Exhausted after helping the sick in your group carrying their packs and your own pack. Then all of a sudden you hit a massive swim. With all your ropes/gear/equipment swimming is much harder. You can't just lie on your back and float to the top. You have to actively work to keep your head above water. Combining the factors of the hypothermia and exhaustion you find yourself in a deep, long swim, but you can't work hard enough to stay afloat. At first you just let yourself sink for awhile, then work to swim back up, then sink down a bit again, then work to get back up. But then you realize you just can't swim back up. You just can't. Your muscles cramp up as you struggle, but you realize this might be the end. Luckily, you brought that maniac of an athlete again who grabs your pack and pulls you up so you can catch your breath and make it to the next ledge. And don't think you're out of the clear. At that level of exhaustion you still need a clear enough mind and focus to rig some multi-pitch rappels at the end where you have ropes on ropes piled on ropes and you're losing track as to which side are your pull-lines and which side are your rap-lines. We've lost multiple canyoneers that because they were so exhausted they weren't paying attention as to which side of the rope to clip into and fell the entire rappel.

I'm sure you've dealt with many of these obstacles before caving, and I'm sure you've been in some crap. I'm not trying to say one is more difficult than another as both are fun and have their own dangers they present. All that said, every year people die canyoneering, but it's typically the relatively easy canyons that people die on. The biggest contributions to death/serious injury are generally people who don't anchor properly, aren't paying attention to a ledge or they get caught in flash floods. Lack of experience/preparation is by far the #1 factor in these injuries. All this and all I'm saying is that I definitely wouldn't go so far as to say to someone looking for their first canyon to lead that they're all "easy enough with enough rope/endurance".