His bondage had softened him. Irresponsibility had weakened him. He had forgotten how to shift for himself. The night yawned about him.

I do not live for what the world thinks of me, but for what I think of myself.

As one grows weaker one is less susceptible to suffering. There is less hurt because there is less to hurt.

Strength is an empty shell.

There is an ecstasy that marks the summit of life, and beyond which life cannot rise. And such is the paradox of living, this ecstasy comes when one is most alive, and it comes as a complete forgetfulness that one is alive. This ecstasy, this forgetfulness of living, comes to the artist, caught up and out of himself in a sheet of flame; it comes to the soldier, war-mad in a stricken field and refusing quarter; and it came to Buck, leading the pack, sounding the old wolf-cry, straining after the food that was alive and that fled swiftly before him through the moonlight.

Fear urged him to go back, but growth drove him on.

...men, groping in the Arctic darkness, had found a yellow metal, and because steamship and transportation companies were booming the find, thousands of men were rushing into the Northland. These men wanted dogs, and the dogs they wanted were heavy dogs, with strong muscles by which to toil, and furry coats to protect them from the frost.