he just got lucky, say what you will about Roseanne she was pretty good about picking writers that weren't the normal LA posioned faggots they had infesting every other tv show at the time. She wanted unique voices and talent and thats why a high school dropout and manual laborer from canada got a job working in hollywood, and he used that to springboard onto SNL and the rest is history. If you notice a lot of outside the box types got their first gig from roseanne and they usually ended up moving on to becoming legends in their own right, at least a lot more often than the Harvard educated faggots working on the simpsons or friends or seinfeld.
