In business why do people avoid learning what they don't know?

In my mentoring practice I run across many entrepreneurs and executives who don't want to know what they don't know.
Of course, in business not knowing can be disasterous.
Why is that?
 
In part, it's because when people admit that they don't know something they believe it's a sign of weakness or incompetence. The truth is, however, that admitting one doesn't know is a sign of strength. Because it's only after admitting that, at least to ourselves, that we can then do something about it, isn't it?
How can we ever learn what we don't know, especially if that lack might hurt us, when we won't admit that we don't know in the first place?
 
Another part of why people avoid dealing with what they don't know is because what if what they discover invalidates what they already know? What if what they're already doing won't work?
Although discovering that might be very, very uncomfortable wouldn't it be better to find out sooner rather than later?
 
Check out Executive Mentoring for help discovering what you don't already know.