Everyone loves Frank, but to me his relationship with his son was always something that damn near ruins him.
Just how responsible is Frank for the way Ziggy turned out? Because on the surface Ziggy looks like a helpless screwup, but he was actually pretty smart and tech-savvy, there is definitely potential in him, just outside of the docks. The Mercedes robbery got him in jail, but he also handled that pretty well (minus the showboating) before it blew up in his face.
What I'm getting at is that Ziggy is just Namond who never found his Bunny Colvin. Ziggy desperately tries to fit in to the docks, to be a real stevedore, but he can't. He should have gone to community college like his brother, he wasn't suited for that life, and I feel like that's where his father failed him - I believe that the neglect he faced from his father as he was growing up just made him want to be a dockworker more, to finally get his father's attention. I don't think Ziggy is a hopeless loser, I just see him as someone who desperately lacked his father's time and attention, who was constantly too busy with the union, dredging up the canal or whatever. If only he paid his son the attention he paid to the union, who knows where Ziggy might have ended up.
I can't help but blame Frank for the way Ziggy is, and I don't believe it's an uncommon theme, where supposedly great men fail at being a good parent. Anyways, I just feel bad for Ziggy, especially since he reminds me of a friend. David Simon said it himself, everyone knows a Ziggy.
Edit: grammar mistakes