However fit and experienced a mountaineer you are, scaling Mt Everest without Supplementary oxygen, and at speed, alway's poses a risk to the body.
This is what Ueli was trying to achieve, reaching the summit, Alpine style, at speed, or quicker than was advisable.
Last year, a very interesting scientific programme was shown on the BBC, whereby medical academics from one of the main Oxford colleges, undertook blood oxygen experiments on various multiple Everest summiteers, and noted Sherpas, throughout their journey up the mountain.
Even the most experienced climbers showed dangerously low red blood count, when pushing themselves to the limit above Camp 3, approaching the 8000m Death Zone.
Some of the climbers simply did not realise the extent to which their bodies were shutting down, due to blood saturation levels.
A few of them felt physically and mentally strong, but were wise enough to listen to medical advice, and return to safety.
There are still only a few climbers who have successfully reached the top of Everest without using bottled oxygen, Reinhold Messner being the most famous.
Treat Everest with disrespect, and you may live to regret it.