Some parents, I have discovered, believe in the parenting slot machine theory. They hold fast to the notion that some parents are simply lucky, meaning that chance and chance alone determines whether one has easy children or difficult children. This parenting slot machine supposedly pays some parents and cheats others. With rare exception, parents with well-behaved kids tend to put no stock in said machine. They believe their children are well behaved because they discipline them properly. Parents with problem children are likely to believe in chance. They believe their children carried baggag…