While at Red Rock I dropped a Smart Water bottle between some boulders and was unable to retrieve it. The fact that I had a second one might have saved my life that day.
The scary thing is that when I packed the water that way, I totally wasn't trying to create redundancy, I was trying to balance my pack by splitting the water weight between the two bottle containers on the two sides.
At the Grand Canyon, the first half is the easy one. It lulls you into thinking you are doing great. It's nice and cool and downhill. Once you get to the bottom, the real work begins. It's 100 degrees with no shade, and any slight problem on the way down it going to be heavily magnified on the way up. If you didn't hydrate or eat on the way down because it felt so easy, you're in trouble once you hit the bottom.
Back to the original subject - there were signs telling people to look out for someone who had fallen off a boat tour in the Colorado River a few days prior. There was also a pair of hikers who had either taken a wrong turn, or had taken a scenic route near the bottom. All three died.
Probably the most useful mantra from the prepping community that gets burned into your brain is "two is one, and one is none".
I hiked down into it a few years ago. I feel like I'm a well-prepared person. On less than a day mountain hikes, I always bring about 1500 calories worth of bars, 2.5L of water, a flashlight, multitool, and something warm if it's cold. It adds a bit of weight but I feel at ease with some backup tools. I made my way down to the bottom (easy) when I realized I was already out of water. WTF I said and I opened my camelback and behold, there was a hole. When I had sat down for a short breather, a really sharp rock had stabbed right through my bag and water bladder with ease and the the bag completely drained.
I pushed my way back up but it was very hot and I think I hit the first or 1.5 stage of heat exhaustion. Like the article, my brain felt like mush and I felt a massive struggle to move. Luckily, there's a spring or some kind of water source midway or so and I just drank a solid amount of water before moving on to the next. I ended up making it ok but it definitely was uncomfortable thinking you were going to dehydrate as you went up.
Random story but I just wanted to share that you can prepare all you want and sometimes life still tries to kick you in the butt. These days I carry a small garmin device that can call a helicopter anywhere in hte world. It costs a bit but it's worth the peace of mind that if I manage to injure myself to the point of being unable to move, I can call for help.