Archimedes paused at a fork. The stimulus was a soft blue light. In the past, turning toward the light resulted in a bitter pellet (), while turning away led to a sugar drop ( Positive Reinforcement ). Elias watched the tiny brain at work. This was the Active part of the principle: Archimedes had to engage with his environment to change his outcome.

He looked at "Subject 42," a clever rat he’d named Archimedes. Most people thought Archimedes was just running a maze, but Elias saw a complex dance of . Every time Archimedes reached a junction and turned right, he wasn't just moving; he was testing a hypothesis. "Go on," Elias whispered.

"That's ," Elias noted, scribbling in his journal. Archimedes was increasing his activity because the expected reward had vanished. It was a stressful moment for the rat, but a vital one for the data. Elias realized that behavior is most persistent when the learner is actively trying to solve the "puzzle" of their environment.