Being a know it all means never having to check facts or do a background check on the people who work for you.
To give a historical example of what happens with a know it all attitude we can look to an event prior to the commencement of the Second War War.
The Wehrmacht had printed a French edition of it's primary work on the theory of armored warfare and gave copies of them to the French Army for distribution to their garrison libraries. A year later the German military attache went through the libraries to see who checked out the book. Most copies had never been touched. The few that were checked out had been read by lowly lieutenants.
The leadership of the French Army believed that they knew it all.
They lost the war of 1940.
Of course past performance is no indication of future results.
Any questions? (Not in French, please.)