One Grain Does Not Fill A Sack But It Helps

Ignoring the sweat that threatened to drown him, Mark let loose another punch at the punching bag. His muscles ached but he pushed past the pain, knowing he had to win his next match at all costs.
Months ago he suffered an injury in the boxing ring and ever since had been recuperating from it.
And next week is his come-back match. Once acclaimed as a world-class boxer, he needs to show them that he still has what it takes.
So ignoring the fatigue he could feel building up in him, he threw another punch, knowing that if he kept doing this, his stamina and strength would return.
Gregor his trainer looked at him then told him to take a break but he let loose another punch, knowing that while a grain does not fill a sack, yet it helps.
So silently, he told himself, "I'm not stopping anytime soon. I need to punch harder," determined to keep the punches going for as long as he had the strength