Soundtracks for BG:EE, SoD, BG2:EE, IWD:EE, PST:EE are now available
in the Beamdog store.
Actually wild mages surge 100% of the time, but the surge fails 95% of the time.
I'm speaking here purely about how the fictional AD&D world would be.
In AD&D, mages have to cast spells just right or they fail. They have a mental component, verbal, arm waving, and if they make one mistake or if they get interrupted then the spell fizzles and fails.
A wild mage then should be constantly doing multiple wild surges whenever they cast a spell but the surges are always failing except 5% of the time one of the wild surges goes off successfully. On the wild surge table one of those said two go off which means two of the wild surges don't fail that rare time.