Bad raiders lament, “If only I had better gear then I could do more DPS”.
Good raiders know that no amount of gear will help your DPS if you only spam one button for the entire boss fight.
Bad raiders assume their lack of gear stops them from doing ample DPS, and that they don’t get invited to raids because they aren’t well geared.
Good raiders gear themselves up with ease doing 5-mans, and learn how to play their class properly (hint: reading what your spells do helps immensely). They are invited to raids often because they come prepared, don’t hold up the raid, and carry their weight.
Bad raiders depend on their guild to provide them with every piece of gear and every dungeon run they wish to participate in.
Good raiders use the built-in LFG system, along with any server-specific group forming channels to find groups on their own, and build their social network.
Bad raiders complain that PUGs are full of idiots who are impossible to complete a dungeon with.
Good raiders know that the bad raiders themselves are those idiots.
Bad raiders don’t move out of fire or void zones.
Good raiders know that no matter how easy Blizzard makes it to get the highest tier gear available, the bad raiders will still die to standing in bad stuff.