All of a sudden he decides its time to learn fire magic. In fact the more he studies and learns of fire magic the greater the chance that he will lose some of those finer details of scimitar mastery or alchemy or any of his other skills. It's a balance. Not only will his learning curve be greatly affected the more he tries to learn, but he does risk the chance of forgetting something else. Now he must go and re-practice his scimitar skill.
Some magic is learned fairly easy.
And with having the ability to gauge the power of your magic, as you grow more experienced you will be able to focus more power and have more powerful spells without ever finding new ones. Research is the key to new spells. And this isn't like EQ where you need to find some random drop items and combine them. This involves, questioning, exploring, questing and experimenting to find new spells. There is a much larger factor that plays into magic as well, unfortunately that is the one I can't talk about just yet.