In the last two episodes we looked at aspects of flow, whether seeking the euphoria as an escape or chasing it as a performance tool. But there's an area of climbing where flow won't be enough. The objectives are too long, too complex and too unpredictable.

At altitude everything becomes harder, your muscles ache under the lack of oxygen and, as Rick Allen has found more than once, your mind can wander.

Rick is one of the world's most accomplished high altitude mountaineers. He's climbed several 8000m peaks, including a new route on the north face of Dhaulagiri. In 2012, together with Sandy Allan he made the first complete ascent of the Mazeno Ridge on Nanga Parbat. The Mazeno is the longest ridge on any 8000m peak, with more than 10km of climbing over eight 7000m summits before the final push. Rick and Sandy spent 18 days on the route, running out of food and water and pushing themselves to their mental and physical limits. The ascent won them a Piolet D'or in 2013, although Rick says the recognition from the climbers he respected was more valuable to him than an award.

Last July Rick was the subject of an unusual rescue on Broad Peak. After attempting the summit solo, he became disorientated on the descent. His hallucinations saw him discard his rucksack and take a fall down the face before he was spotted by a drone sent to search for him.

The episode has given him a chance to reflect on the risks he takes in the mountains and his partnership with Sandy, who told him in no uncertain terms that he'd made the wrong call on Broad Peak. Rick realised he needed that other voice to ground him, to help him see what was real. Yet he and Sandy are very different characters, chasing the same dreams.

For more information on their ascent of the Mazeno Ridge you could read Sandy Allan's excellent book, In Some Lost Place.