Blindness

In reference to
http://johnkstuff.blogspot.com/2010/03/direction-3-what-you-need-to-be-good.html
"There were a number of directors making Terrytoons, but it's much harder to tell their directors apart than it is for us to distinguish Warner Bros. directors. There are of course a couple people who can tell the difference, but they are as rare as good directors are."

If you sit and watch Terrytoons in an era, you can see the different directorial styles.
Lack of exposure leads to failure to see the differences:
http://cartoonsof1939.blogspot.com/search/label/Terrytoons