why did White Fang always win his fights?

White Fang never lost a fight because no dog could ever make him lose his footing.

He never knew defeat.  His early training, when he fought with Lip-lip and the whole puppy-pack, stood him in good stead.  There was the tenacity with which he clung to the earth.  No dog could make him lose his footing.  This was the favourite trick of the wolf breeds—to rush in upon him, either directly or with an unexpected swerve, in the hope of striking his shoulder and overthrowing him.  Mackenzie hounds, Eskimo and Labrador dogs, huskies and Malemutes—all tried it on him, and all failed.  He was never known to lose his footing.  Men told this to one another, and looked each time to see it happen; but White Fang always disappointed them.