Why does Henry tie a pine-knot on his right hand?

Henry ties a burning pine-knot to his right hand in order to keep himself awake. He cannot fall asleep or the wolves will overtake his small camp.

But this time, before he dozed again, he tied a burning pine-knot to his right hand. His eyes were closed but few minutes when the burn of the flame on his flesh awakened him. For several hours he adhered to this programme. Every time he was thus awakened he drove back the wolves with flying brands, replenished the fire, and rearranged the pine-knot on his hand. All worked well, but there came a time when he fastened the pine-knot insecurely. As his eyes closed it fell away from his hand.