Weight is definitely a complicated issue for many people, which should be evident by the amount of research still being done on the subject of weight gain and loss, and what really constitutes a healthy weight for people.
Weight itself is not a complicated issue. Eating healthy is not a complicated issue. Staying in reasonable shape is not a complicated issue.
Unfortunately, many people overcomplicate it. It is easy to observe that the people who overcomplicate it, are the same people who believe that since it's simple, it should be easy.