Complex sentence: Even for the able, the Everest North-East ridge is a recognised as a challenge, which is why it is so hard to rescue someone who has become incapacitated--it is beyond their ability to save them in such a difficult spot.
Split into simpler sentences: Even for the able, the Everest North-East ridge is recognised as a challenge. It is hard to rescue someone who has become incapacitated and it can be beyond the ability of rescuers to save "anyone" in such a difficult spot.