The most important technique to master to play Blues

I think all of us here have really missed the boat on what is probably the most important technique to master. I don't understand how John G. could have overlooked this in his otherwise superb series of books.
www.guitarplayer.com/lessons/1014/jesse-phillips-shows-how-to-make-guitar-face--video/51153

I seriously think that the next book in the series should be "Blues Faces You Can Use."