How does Charlie's attitude change after the operation?

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.