Reading the primary source documents of the Donner story (ETA: based on the Breen diary and other journals, members' letters, etc.) is wrenching.
A series of bad decisions -- the oversized wagon, the unproven cutoff. All along the route, their story is full of, 'NOOOOO!" moments for the reader.
The Donner party came within just a short distance (IIRC, a couple of hundred yards) of making it over the mountain pass that blocked them. They turned back to rest the oxen for another attempt, then someone lit a fire, the party chose to warm themselves before making another effort, by the time they realized what they'd done, it was too late.