Sure, mountain climbers require aclimatisation to ascend to great heights.
This takes
days, even weeks, and even then, the individual might not succeed.
Every time I've been in the Hypobaric Chamber, and I've probably done a dozen runs at altitude without oxygen now, I've lasted less than 4 mins before requiring assistance (whether that was deciding to put on my mask, or requiring help from another - which is normally wiped from my memory). And that was whilst on 100% Oxygen during the climb. And I'm pretty average, meaning others last less, and others have lasted maybe a minute or two longer.
The rapid decompressions are even more fun, actually alarming, but if you're about to eat I won't go into that right now.
