Winston is one of Skipper's remaining sons. He lives with his wife at Skipper's home. It is Rosie who cares for Skipper daily in the wake of jacob's death in a storm thirty years earlier. A reasonable explanation for Winston's characterization would be oppression from being tied so closely to an oppressive father who was brutal enough to drive his son to his death.
In Michael Cook's Jacob's Wake, it appears that Winston's characteristics of lethargy, cynicism and bitterness are related to his sister's hateful behavior and the actions of his sons to some degree, but Winston's father's treatment of Winston harms him more than the others.
Thirty years before, Skipper lost his son (his favorite son) in a seafaring accident (that also took Skipper's legs). On the day Jacob died, Skipper gave up caring for the rest of his family. He blames himself for Jacob's loss, explaining (we can infer from the following quote) that he was only partly responsible. Thirty years later, he is defending himself to his dead son, while he is in a delusional state:
I nivir sent the starm, Jacob. Ye can't blame me for that.
Skipper's wife, Rachel (and Jacob's mother) never forgave Skipper, and this may well have fed his sense of guilt. It was at this time that the family lost its direction, for Skipper stopped caring for anyone else but Jacob (who was beyond help), ignoring those in his family that he could have helped.
Skipper, in a confused moment when he addresses his dead wife asks if, in such a world, they should ever have "made" a daughter, or a son...this could apply to Jacob, but also to Winston; for Skipper's disappointment in his surviving son is obvious.
For Winston, much seems to rest on his father's discontent with him—that Winston wasn't more like Jacob. When Mary starts to berate Winston, he tells her:
Oh yis. Sneer all ye want. Talking to me father is always hard work, like reading hist'ry backwards...I wish sometimes that I could have been the son he wanted.
When Mary vindictively says that if this had been the case, Winston would be dead just like Jacob, Winston heartily agrees—leaving the reader to infer that he wishes he had died with Jacob rather than being left behind, constantly reminded that he can never measure up to Jacob—his brother, frozen in time, a god-like figure in Skipper's mind. This beats Winston down.
Winston's identity as Skipper's other son is lost as Skipper often speaks to Winston believing he is speaking to the long-dead Jacob. To Winston, Skipper says:
Ye'll check her moorings, son...That's good, Jacob.
This is the only time Skipper cares for him...but it's not really Winston at all:
I cares for ye, Winston...
And when [Skipper] thinks I'm Jacob, so do he...
With his own sons who have not amounted to much (unsuccessful, corrupt, lazy, etc.), Winston drowns himself with an endless stream of beer, fighting the realization that the family really is "adrift," as Skipper notes in a rare lucid moment. With Mary's hypocritical and scathing criticisms regarding the unethical and immoral character of all the men in the house, and finally Alonzo's forgery of Winston's name on Skipper's commitment papers (at Wayne's urging), we see Winston nearly destroyed.
But while his sister and his sons contribute to Winston's sense of demoralization, it is Skipper who has driven Winston to this level of despair for the past thirty years. And though it was Skipper who drove the men onto the ice after more seals that fateful day (even though he knew the conditions were dangerous), he has retreated to a fantasy world where Jacob is alive rather than assuming the responsibility for his obsession and selfishness...or soothes his guilt with vast amounts of rum. Winston pays the price for a sin that he never committed: other than, in Skipper's eyes, not being Jacob.