Walking down is harder on your knees, he probably was in too much pain. That's my guess anyway.    After a 5 hour hike up a mountain in Argentina one of my knees gave out, no reason, just not enough conditioning before the trip I guess. I finished the hike up the mountain with some ski poles and my left leg. So yay, got to the top! :)  However, it took me 7 hours to get back down with LOADS of painkillers that did sweet fuck all.  But I weighed about 105lbs 5'3" at the time so I had no extra weight to deal with. My knee took 3 weeks to heal up after that. Going downhill can suck a lot. Not making excuses - his fat ass shouldn't have gone up in the first place. I'm just thinking why he couldn't get down again, lol.