I think that was one of the things that made me give up on my Fantasy novel: my Magic system didn't make much sense, or rather, it was too simple and there was hardly any "cost" to use it properly.
How did it work? Well, there is all sorts of Elemental Magic in the land of Corim, such as Fire, Ice, Lightning, Nature, Healing and so on; and a Mage can learn one type or multiple ones if they wish (although, I'd imagine that learning multiple ones would take longer) When a Mage is casting a spell, they simply have to focus on whatever task they have (Mages in training are taught to close their eyes to help them with this, while an advanced Mage doesn't have to), their eyes glow and they see their target in whatever color that Magic is associated with while everything else around them (from their POV, not literally) is in black and white. Once they are focused, they simply just thrust their hand/s forward and ALAKAZAM!
And seeing as you have to keep calm and focus to perform Magic, there really isn't such a thing as insane Mages in Corim as their spells with just backfire.