I think, Omar's killing was one of the most intelligent scenes in The Wire. They tried to get at him in million ways, which made him to be careful in some special way, which led to a certain blindness. "The game" as they call it here ("business" in The Godfather) is a like a Russian roulette. No-one's safe. No-one. You can't predict anybody's fate. Who would have thought that Poot will be the one who survives from the old crew. You just can't "keep the devil way down in the hole". If you believe you're smart, you have lost already.