Go figure. The guy throws 1-hit ball for 5.2 innings against the Dodgers, gives up zero earned runs, and gets tagged with the loss. If you're keeping track, it's his 9th consecutive loss. He last won on July 16th. Since then, he's 0-9. There have been some very bad outings, but overall, Zito's ERA during that streak is 4.48--not great, but not 0-9 bad.
I've written before about the good Barry/bad Barry syndrome. You may have heard that his career record when the team scores 4 or more runs is 109-6. But when the team doesn't score--and the Giants have only scored 11 runs while Zito was in the game over his last 12 starts--you get the bad Barry.
I'm no psychologist, and maybe Zito would disagree, but here's a guess: when the team is rolling, Zito relaxes and lets it flow, and he's darned good. When the team isn't scoring, he tries to get too fine, and trouble ensues.
And then, there's the potential that this is all just a bizarre confluence of unexplainable forces, and Zito is the butt of some cosmic joke.
I'm going with the last one.