Great article in the New Yorker that talks about the role that coaches can have on performance. Talks about the role of coaches for top-flight athletes, and looks at a few fields including education and surgery where coaching can move professionals to a new level.

"So outside ears, and eyes, are important for concert-calibre musicians and Olympic-level athletes. What about regular professionals, who just want to do what they do as well as they can"

Read more:
http://www.newyorker.com/reporting/2011/10/03/111003fa_fact_gawande