This article from Science Daily interviews Jim Denison, of the Canadian Athletics Coaching Centre, is full of great points on the need for coaches to avoid becoming complacent, and instead seek to be continual learning and evolution in their coaching practice:
"Coaching is complex, continually changing and influenced greatly by the context, athletes' circumstances and the developing relationship between the coach and the athlete."
"There's good research that shows that when coaches achieve this expert status they tend to want to maintain that," he says, "so admitting that you don't know becomes a threat to their expertise."
"Often the most successful coaches are the ones who are most willing to adopt a lifelong learning approach and to admit that they don't know," says Denison, who advocates "problem-setting" -- determining whether there is indeed a problem, before "problem-solving."
I'd add that a level of humility also goes a long way in coaches - the more you know, the more you know you don't know.