Sure, they might be successful in killing their master and a few others. But the penalty for any violence against a master or overseer was death. And so while they might have a brief victory, all the white men nearby, armed with guns, on horseback, and with dogs, would come running, and would ultimately be victorious. There WERE slaves who rebelled. And always, their fate was the same. Death. Not just for them, but for any who it was thought might have abetted them. Solomon Northup tells of a case of rebellion in the book 12 Years a Slave, and that's exactly what happened. Men of the area patrolled daily for signs of slaves trying to escape, and were always ready with weapons to attack or deal with rebellious slaves.