The Dark Side...
Much remains unknown about materia and its full potential. There are dark whispers, however, that tell of a forbidden branch of the craft that leads to power beyond imagining…but only at great cost.
The forbidden branch may decrease the odds of failure. Not to mention traits may be implemented to lower the odds of failure. Who knows how they will implement it. It may be with every craft there is a trait that lowers failure by 5% and with all crafts the odds of failure for 5th materia is 25%. WE DON'T HAVE ALL THE INFORMATION.