Why does Charlie say he does not like writing in his progress report on the third day?

In the short story Flowers for Algernon, Charlie is a man who has mental challenges. He is discovered by scientists who are working on a project to increase human intelligence, and Charlie agrees to participate. In the early days of his progress reports, he is undergoing various tests to determine his current level of mental abilities.
Charlie equates being able to read and write well with being smart:

I askd pepul and sumbody told me where I shud go to lern to read and spell good. They said why did you want to. I told them becaus all my life I wantid to be smart and not dumb.

In another language activity, they show Charlie pictures of various people and ask him to generate stories to go with them. Charlie lacks the mental ability to create a story from his imagination, which would make writing doubly difficult. His response: "I told her how can you tell storys about pepul you never met. I said why shud I make up lies."
It is clear from the progress reports themselves that Charlie struggles with forming words, but his reflections show that he also struggles with creativity and reasoning. In combination, all of these deficits would make writing an incredibly difficult task, and people tend to avoid tasks that they find difficult. Although Charlie never explicitly states that he does not like writing, it can be inferred from his progress report on this day that this is true.