IDK about coaching. If you've ever been seriously coached for performance (think sports) an effective coach will look you dead in the eye and tell you you're terrible. At work, in technical fields, everyone likes to be liked and shy's away from being a bastard to their peers and reports. Especially if the conditions aren't that great and killing yourself for your current gig isn't giving you windfall returns.

Giving people the tools to succeed or at least being clear to them that they and need to do better is a managers job.