Why are individual case studies (like gage) less useful than other forms of research?

Marian recently made the decision to try to re-wallpaper her own kitchen—which was a mistake given her personality! to compound the mistake, she selected a complex wallpaper pattern that included flowers and trees. each time she put one strip of paper on the wall, she became increasingly upset if there was not a perfect match from the pattern of one strip to the next. if one flower was off by as much as one-tenth of an inch, she would tear down the strip, remove the excess paste, and try again with the next strip. over eight hours after she started this job, she has only succeeded at putting up six strips of wallpaper, which covered about 10 percent of the room in which she was working. marian may suffer from personality disorder.