Artificial intelligence and computer science researchers say getting machines to do the right thing has turned out to be relatively easy. We program Roombas to vacuum our homes, but don’t expect them to brew our coffee. We program robotic arms to sort parts in factories, but not to decide which colors to paint cars. We program doorbells to tell us who is at the door, but not to let them in. Most of our machines do one thing and do it well, usually in error-free fashion. They get the task right.