We're talking about coaching.
Players like Cesc and RVP walked in the door with great technical ability. It's not as if Wenger coached that into them. We've got guys that have been here a long time and still have fundamental flaws in their game. Guys like Djouoru, Bendtner, Denilson, Diaby, Eboue...they make the same mistakes from game to game without correction. Maybe Wenger thinks they're not progressing because the problem is psychological when it's really a technical issue.