After the operation, as he gains intelligence, Charlie's attitudes become much less naive and childlike. When the story opens, he wants nothing more than to please the people in his life, whom he treats as godlike adults.

As his intelligence grows, however, Charlie begins to develop a more a nuanced attitude toward other people. He realizes, for example, the extent to which the workmates he considered his friends made him the butt of cruel jokes. As a result, he begins to feel ashamed of his former self. Further, he no longer treats Miss Kinnian as a six-year-old might his adored elementary school teacher. She moves from an object of awe to a peer he can date and with whom he can have a romantic relationship.

Charlie also begins to discern that the scientists, particularly Dr. Nemur, are not the all-knowing gods he thought they were when he was mentally disabled. He starts to recognize Dr. Nemur's limitations and to realize that, because he is aging, Dr. Nemur has rushed into this experiment in enhancing intelligence with inadequate preparation.

Charlie moves from the situation of child to adult in a very rapid time sequence, and his attitudes change to reflect his greater depth of understanding.

After the surgery, Charlie’s attitude towards people he thought were his friends changed and he saw them as people who ridiculed him because of his low IQ. After the operation he becomes disappointed because the change he expected was not immediate, but his hope is restored and he develops a positive attitude after assurances are made by Doctor Strauss, who tells him that his intelligence will improve as it did with Algernon, the first successful test subject. He develops a strong personality and uses his new developed intelligence to help at the factory. Charlie displays some level of self consciousness as seen through his inability to further communicate with Miss Kinnian. Later on, Charlie’s intelligence begins to wane, but he remains positive and does not regret the process, instead he congratulates himself.

In Daniel Keyes' novel Flowers for Algernon, the main character has an experimental operation to increase his intelligence. After the surgery radically improves Charlie's intelligence, his outlook on life changes significantly. Ironically, these changes are not positive in terms of Charlie's happiness. 

Before the operation, Charlie is functional but moderately mentally retarded. He can hold down a job and take care of himself, but he is not able to discern subtle shades of meaning or recognize the hidden intentions of others. Before the operation, although he wants to become “smart” and feels the effect of his limited intelligence, he is a generally happy person. He values companionship and sees the good in others, even when they are not particularly nice to him.

After the operation, with his increased ability to see beyond the superficial and into the true motivations of others, he realizes that he has been an object of ridicule at the hands of his fellow workers, who he had thought of previously as friends. This leads Charlie to the following observation:

“I don’t know what’s worse: to not know what you are and be happy, or to become what you’ve always wanted to be, and feel alone.” 

With his newfound intelligence, which reaches the level of genius, he begins to work on the problem of his inevitable intellectual demise. Where in his previous life he would have accepted his failure, he now becomes obsessed with the challenge, which he cannot meet.

Finally, his most significant relationship, with his teacher, Miss Kinnian, becomes romantic as his intelligence increases. However, with the rise in his mental abilities he also becomes more self-conscious, with a greater sensitivity to how others see him. For this reason, when he realizes that the positive effects of the operation are going to wear off, he demands that Miss Kinnian not see him any longer. He is willing to give up his most positive and rewarding relationship to preserve what is left of his dignity. The old Charlie never would have thought of things that way.