tips for coping with motivation, dark moments, wind/rain etc on endurance rides.
Read some climbing books maybe - The Shining Mountain, how Boardman and Tasker climbed Changabang. Or Touching the Void if you've not read it. Walter Bonatti's Mountains of My Life - his solo of the Petit Dru Pillar or escape from Mont Blanc.
Cyclists don't know how easy they have it ) I've not read anything that shows how much you can take when it gets properly cold, tough, you're tired, hungry and hallucinating etc in the way mountaineering books can. Maybe there's less of a tradition of writing to pay for trips in cycling and the real hard riders I can think of haven't written books yet. (If I've missed any, would be good to hear of them)