I was running random Stockades on a low-level warrior, when I encountered a mage who was pretty obviously a new player. He wasn't a "bad" player, at least he did not pull mobs and roll need on everything. But his DPS was abysmal for that level.
Obviously, he had no heirlooms, so that made a difference. But more important was his spell mix.
He had Pyroblast, so he was a Fire mage. Except he never cast Fireball! He cast every single other spell in his repertoire instead. Frostbolts, Fireblasts, Frost Novas, Arcane Explosions, etc.
Clearly, this was the wrong thing to do. But when you think about it, there is a certain logic to his actions. First, he obviously saw Pyroblast as a "upgraded" Fireball. After all, why have two spells which hurl giant balls of fire at your enemies? And to be fair, there are specialization abilities which work like this. For example, Mangle replaces Claw for Feral druids.
As for the other spells, why have all these spells if you're not expect to use them? If you think about it, it does seem odd to drop half or more spells from your spellbook.
He is wrong, but he's not stupid. His reasoning makes some sense. And in the absence of easy to understand feedback, it's hard to tell that he's gone wrong.
Whenever people say that the levelling game is too easy, I think of players like this. We experienced players are used to the conventions of the genre, which extends to the abilities used. Ideas like "your best spell should be spammed" are a bit alien at first.
Even if you don't have the best reflexes, understanding those basic conventions can put you head and shoulders above new players who don't understand how abilities in the genre are supposed to work. We've internalized the math and advice that tells us to refresh DoTs when they expire and not before, to spam Fireball, to save instant spells for movement, to divide damage by cast time when evaluating effectiveness.
When you think about it, it is amazing how much knowledge we MMO players consider basic.