Explain why a small standard deviation of the MTBF distribution makes a product, machine, or process a good candidate for preventive maintenance while a large standard deviation does not.

A small standard deviation means that there is a relatively narrow range for breakdowns. With this narrow range, it is easier to predict when failure might occur and, therefore, take preventive action in advance of failure. A large standard deviation implies a wider range of values over which failure might occur, making failure less predictable and preventive maintenance less advantageous.