I wouldn't say you are stupid. My rogue was level 35 when I found out that leathworkers get a specialization, I would imagine most people don't find this out on their own. Of course the better course would have been to take up dragonscale leatherworking at 40 but you can't undo the past. Since you already had mining up, you might have thought about dropping blacksmithing for engineering or jewelcrafting for the nice BoP items. Overall, the game is about having fun. If you are doing that, then you are not doing anything wrong.