As powerful as magic is, it does have drawbacks.
The most common way magic is used is to be wielded as
a weapon. Due to the nature of magic, the effects of
magical spells may not be apparent. Some creatures 
themselves are born of magic, with powers
to ward off magical attacks. Others have other ways
to defeat offensive magic cast upon them. In order to
efficiently use magic to defeat a foe, means being able
to tell if your attacks are having any affect. By 
carefully studying the effects of magic one can
deduce his effectiveness against his enemy. Of course
there is said to be magic which can hide the true
effects of magic from even those most proficient at
this skill. It is said that wisdom may help discern
the effects of spells using this power.