Want to make casting more unpredictable, because, well... magic? Want that unpredictability to still be fair and not just decided off the top of your head?
We have a supplemental rule for you. What happens when you not only lose focus, but do so epically while still channeling your magic? roll your percentile and find out. The results of unfinished magics can be unpredictable and unpredictable can be fun!