I'd say the biggest factor is that its your team. You are emotionally invested in them and when less than excellent play occurs, especially when it costs the team, it is unpleasant or even painful. Other teams have plenty of misplays and errors as well. D-backs fans sometimes call them the E-backs because of their errors. Braun has looked awkward, but generally has played very well. Consider how his fans can recite his only mistakes. Then contrast him with someone like Soriano. Crazy Al has a lot of talent and a quick accurate arm, but he makes some of the ugliest plays in baseball. Or the "fantastic" Fukudome: just seeing about a fifth of the Flubbies games, I've seen him misplay 4 or 5 balls. Wasn't it last year when Tulowitzki had two errors in an inning against us? Really, what sort of player is acceptable? It seems Brewers fans generally want power hitters, who also have a fairly high average and play excellent defense. Its like wanting your significant other to be beautiful, have a great personality and be wealthy. Yes, it does happen. No, not often. If a player is excellent defensively, but not great offensively, then there is a lot of moaning about that.