FIP, or Fielding Independant Pitching is basically an adjusted ERA aimed to take good/bad luck out of the equation. FIP looks to separate a pitchers performance from that of his teammates and ballpark factors. In order to do so, calculating FIP removes balls in play, which the pitcher has no control over. Doing such can even the playing field. The end result is a number based on the same ERA scale, yet it is much more indicative of how a pitcher has pitched.
As with almost all statistics, there are outliers that can last 50 games, a season, or in Matt Cain’s case- an entire career.