Because of the Thin layer of oxygen one may feel weak despite carrying the artificial oxygen.
At an elevation of 8848.86m high, Everest is the world’s highest peak. The higher the altitude, the lower the oxygen is. So, at Everest which is at the highest elevation, the level of oxygen is extremely low. A normal human being finds it difficult to live at that level of oxygen. Similarly, the elevation above 8000m is considered the Death Zone, where the air is thin. Because of the Thin layer of oxygen one may feel weak despite carrying the artificial oxygen. Therefore the oxygen level at Everest makes it harder while Climb Mount Everest.