I understand your point but self discipline is a trained habit. Some children grow up having received little to no training. Once adults, changing the dysfunctional conditions of their formative years is not something that happens over night.
As a child raised in a very dysfunctional home, I can attest that a person can acquire self-discipline to get ahead in life...if one desires it. It's really a choice. I'm not trying to be hard...just deflecting age-old excuses for laziness.