About 50 years ago I read a short story about a person sent to live on the moon with a robot helper. Rather than a traditional high IQ athletic astronaut, the man is an average guy in every way. The project is a test to learn how an ordinary person could cope with the rigors of colonizing a new world, thus aiding in planning future interstellar colonizations by ordinary pioneers.
At the beginning the man makes many mistakes and suffers a variety of accidents and injuries caused by his own clumsiness and other short-comings. Without the robot helper he would not have survived. However, as time passes the man becomes much more physically fit and competent in all aspects of survival. However, at the same time he notices the robot seems to be less and less helpful, making its own mistakes with increasing frequency, often resulting in injury to the man. The man finally realizes that the scientists who designed the project anticipated that with experience his competence would increase, thereby decreasing his value as a test subject representing ordinary and inexperienced pioneers on a new planet. Therefore, the scientists programmed the robot to compensate for the man's increasing competence by becoming less competent itself thereby preserving the desired test environment.
The man decides he would be better off without the robot and pushes it into a deep crater, presumably destroyed by the fall. For a few months everything goes well. Then, without warning, the robot reappears, having climbed out of the crater. The robot seeks to inflict on the man at one time all the many problems and injuries it should have caused during the months the robot was absent - which of course would kill the man. The man outwits the robot (I forget how) and destroys it for good.
I would be very grateful if someone can identify the author and title of this story.