I can't find the bit where he talks explicitly about this as I've lost access to the book I read it in (and don't even remember the name). I'll see if I can dig it out.

In the passage I am unable to find, he gets into the issue of having a worker making widgets, and another worker checking the widgets. In our world this would be a developer and a test author. He states that this reduces quality: the maker knows that he can make poor parts when he is in a hurry, because the tester will catch them; the tester knows the worker personally, and trusts that he will make good parts, so doesn't have to be very thorough. Instead, we need the worker making the widget to be responsible for its quality, and further to be empowered to do so.