after deciding not to eat his lunch, how does the man's outlook of his situation drastically and briefly change?

After deciding he'd made a mistake by not building a fire and thawing out the man chuckles at his own situation........

"He tried to take a mouthful, but the ice-muzzle prevented. He had forgotten to build a fire and thaw out. He chuckled at his foolishness, and as he chuckled he noted the numbness creeping into the exposed fingers."