Roger, I cannot count the number of times my left hand has been on the business side of the chisel when it slipped and cut something. The difference is that until recently, my chisels were never very sharp, so the cuts weren't very bad. The danger of it has finally slowly started to sink in, but too often, I still find myself steadying something with one hand and coming at it with a chisel in the other hand.
You are not the first or last to have this happen to you. By labor day, it will be a distant memory.