The rats and the humans had to look at a TV screen and press the lever anytime a dot appeared in the top half of the screen. The experimenter didn't tell the human subjects that's what they were supposed to do; they had to figure it out for themselves the same way the rats did.
The experiment was set up so that 70 percent of the time the dot was in the top of the screen. Since there wasn't any punishment for a wrong response, the smartest strategy was just to push the bar 100 percent of the time. That way you'd end up getting a reward 70 percent of the time, even though you didn't have a clue what the pattern was.
That's what the rats did. The just kept pressing the bar every time the screen changed.
But the humans never figured this out. They kept trying to come up with a rule, so sometimes they'd press the bar and sometimes they wouldn't, trying to figure it out. Some of them thought they had come up with a rule, which they then used to tell them when to press the bar and when not to press the bar. But they were deluded. They hadn't come up with the rule at all, and the rats ended up with lost more rewards than the humans.