At thirty days into the new global peace, Clu was monitoring his citizens' thought patterns at his console in what used to be the ENCOM tower. And he did not like what he saw. "Rinzler!" he called.
"Yes, sir?"
"Get me Alan Two."
"Yes, sir."
Before the new order, Alan Two used to be Jet Bradley, in charge of the digitization program at ENCOM. After his rectification, now wearing an armored program outfit marked with a tangle of orange lines on multiple layers, he was in charge of brainwave translation. He entered the room and approached Clu's command console.
"Alan Two reporting, sir." he said.
"Look at these signals." said Clu. "Tell me. What do you see?"
"They are unhappy, sir." Alan Two answered.
"I can see that." Clu added. "What I want to know is why!"
Alan Two pondered over the waveforms for some instants.
"They remember, sir." he started. "We gave them incorruptible bodies and eliminated death, but they still have emotionally charged memories of their previous imperfect lives. They long for them. They long for imperfection."
"That is certainly illogical, as history shows they longed to overcome those problems." Clu replied.
"Those are the symptoms of nostalgia." Alan Two said. "Human minds get used to habitual forms of sensory input, to the point that they miss them when they are absent."
Clu considered the new information for a couple of seconds. "Maybe the answer lies in their way of conceiving pleasant and unpleasant stimuli. What does their literature say?"
"Well, sir - you may find this interesting." Alan Two began. "The vast majority of the books I scanned contain the idea that the most unpleasant conceivable stimulus is an eternity of excruciating burning pain distributed all over the body, coupled with an overwhelming odor of putrefaction and the screams of billions of other people suffering the same fate."
"That makes sense." said Clu. "But...?"
"But," continued Alan Two, "the same books suggest that the most pleasant conceivable stimulus is an eternity spent contemplating... light."
"Now, that does not make sense." commented Clu.
"Indeed, sir." Alan Two started again. "Trying to deduce the polar opposite of the most unpleasant conceivable stimulus, I discovered other literature explaining the role of the nucleus accumbens, the most frontal part of the brain, in the perception of pleasure. That could be the most pleasant conceivable stimulus. An eternity of electrical stimulation of the nucleus accumbens in the brain."
"Thanks, Alan Two." said Clu. "You've been certainly useful. Adapting the rectification process to the new information will require some recoding."
In short time, every rectified citizen was implanted with an array of electrodes that provided constant stimulation to their nucleus accumbens, providing them with perpetual artificial pleasure.
Humanity lived happily ever after.