During those eight years, he learned to count cards while serving time for his hand in torturing and abusing Abu Ghraib prisoners (a real tragedy that surfaced in 2004). In a sense, William is spending his days in sort of afterlife, given that his former life was spent in a military prison. William Tell (played by Oscar Isaac) lives a sad life, moving from one motel to the next, living out of suitcases and covering all the furniture in bedsheets.
Gambling films aren't usually bloody, but The Card Counter is.