A choice between two unbearable options.
The loan hiker's arm was wedged in a crevice when he slipped and fell. He didn't have the strength to release himself. Each movement wedged his arm more deeply into the crevice. After several days without food and water, he was left with a Sophie's Choice: continue to wait for help and possibly die, or use the serrated blade of his pocket knife to cut off his own arm and climb to safety before bleeding to death.