Did a final training hike around Lake Geneva the other day. Five hours in the rain with full packs, 14 miles or so. Felt fairly good about it until realizing: "So instead of around a lake, it's 4000' of vertical. Take a break, put your pack on and do it again in the afternoon, racing against dark when the temperatures plunge towards freezing. Sleep in a tent, wake up at 5AM to do it all over again. For 4 days. Oh yeah, at 10,000'."