A machine/robot can be more stable compared to a human. An example would be the DaVinci robot, which is used worldwide to perform operations, especially when it is a risky and difficult operation. However, these robots are operated by a doctor which needs to be trained and assisted during the operation by engineers that can intervene in case something happens.
There was a case a few years ago, when one of the DaVinci robots killed a patient during a heart operation. The medical doctor was never trained to use the robot and did not know what to do when the robot went rogue. Furthermore, the engineers were not in the room. So you can say the accident was also a human error.