xFIP is a simplification, definitely not perfect, as pointed out already. But it does a good job of removing luck, natural variation, defense, and park effects. Those are not the only factors that influence ERA, however, but they are large ones. This is a sound bit of advice. As with any stat, don't trust it on its own, but (x)FIP is a significantly more accurate stat imho in evaluating pitching, since it doesn't gloss over major considerations the way ERA (and ERA+) does. This happens very very rarely. A routine play in my opinion is an easy ground ball hit directly at a fielder. If a fielder misplays it, it goes down as an error. Unless the official scorer is blind or something. People are acting like this happens all the time. It hardly ever happens. So then the question you have to ask yourself in terms of preference is, 'Since it happens rarely, does that mean I/you/we should penalize a pitcher for it?' If your answer is 'yes', since in your estimation it's a negligible occurrence, then you'll probably be happy to stick with ERA/+, etc.. However, the example provided of the 2007 Marlins v. 2007 Rockies (the 2007 Brewers certainly fall in as a strong example, too) seems to indicate that this happens much more than 'hardly ever.'