What does this quote mean The difference between a successful person and others is NOT a lack of strength or knowledge but rather in a lack of WILL?

It implies that the truly successful people are those who are driven, determined, resilient and motivated. Innate ability is worthless if not co-existent with these attributes, causing even those who are naturally intelligent or otherwise talented, but inherently lazy, to fail. Those with immense will to succeed, however, will do so no matter the adversities they face.