Can anyone please explain the reasons for Matt Schaubs inconsistency this year?

I've only seen one Texans game this year. The one against the Redskins where Schaub was great. But other than that he's been lackluster or just bad in all the other games. I guess some of it can be attributed to Andre Johnson's injury, but Schaub wasn't good in Week 1 vs. the Colts when Johnson was still healthy. Is there a reason why Schaub hasn't been very good? Is there a reason to think the Texans ping game will turn it around this year?