>>2835362
>I've been with so many super fit people who bonk halfway to the summit because they can run a 20min 5K and think that means shit on the mountain
well yeah, they've practiced anaerobic zone 4 training.

mountaineering is "can you uphill zone 2 nonstop for 8 hours in a row". And that's before the mental endurance game of dealing with discomfort in bad weather, etc.