A prejudicial belief that products, systems, software, etc., that were not developed within a company or organization are not as suitable or well made as those that are created in-house. I think the boss's not-invented-here-syndrome stems from experiences he had using third-party software in his previous business, which apparently cost them thousands of dollars trying to implement.
See also: syndrome
Farlex Dictionary of Idioms. © 2015 Farlex, Inc, all rights reserved.