Combat is supposedly going to be tough enough even WITHOUT spells misfiring. A misfiring chance would make people shun the magic system Larian has crafted - if magic is going to be unreliable, then people won't rely on it.
Physical attacks aren't 100% accurate neither (unless the percent showed when attacking a enemy is just a pointless lie), a misfire doesn't need to happen every other time, casting can be a "safe bet" there is just the fact that such thing doesn't really exist
The effect shouldn't something totally random tho', it need to make sense with the school of magic or element (if we can really speak of "sense" in the context of magic)
