Many moviegoers love watching for big-screen mistakes: Roman slaves occasionally wearing watches in "Spartacus"; Julia Roberts picking up a croissant but biting into a pancake in "Pretty Woman."

But viewers who think they easily spot these continuity flubs probably miss more than they find.

As for the experts making the movies: They shoot scenes on different days and try to match them up. But because of all the minor details, it's not that surprising that they don't notice a few accidental mistakes, Daniel Simons says.

In "The Invisible Gorilla," Simons and Christopher Chabris explain that such failures are called "change blindness": "People are 'blind' to the changes between what was in view moments before and what is in view now."

So for every error spotted in a movie, there are probably others that are not, the authors write.

There's a reason for this blindness: "In the real world, objects don't abruptly change into other objects, so checking all the visual details from moment to moment to make sure they haven't changed would be a spectacular waste of brainpower."

"The Invisible Gorilla" explains in easy-to-understand terms how our brains make mistakes. Sometimes, the gray matter doesn't notice what's right in front of it. Sometimes, it confidently conjures up memories of people who weren't at an event we recall. Sometimes, it seems to assure us that we know a lot about something when we don't — and we make quick decisions based on our "gut" reaction.

"We tend to trust our intuition a lot more than we should," Simons says. "It's what our brains are built to do."

Simons, like Chabris, is a cognitive psychologist. He grew up in Olivette and graduated from Ladue High School. After earning his doctorate at Cornell University, Simons taught at Harvard University, where he met Chabris. Now married with two children, Simons, 41, teaches psychology at the University of Illinois at Urbana-Champaign.

Back in his hometown last week for a book signing, he acknowledged how confusing it can be for readers to sift through the increasing number of popular books that tell us about individual and group thinking and psychology. Malcolm Gladwell's "Blink" and "The Tipping Point" became best-sellers and household words. Yet, a reader confronted by titles such as the new "Being Wrong" by Kathryn Schulz, "Wrong" by David H. Freedman or "Predictably Irrational" by Daniel Ariely might justly be confused about what to think.

"It wasn't our goal to write the anti-'Blink,'" Simons says. "That's a wonderful, fun read. We're not saying that gut instinct is always bad. But there are some intuitions we trust more than we should."

So rather than base decisions on intuition (such as what books to buy, perhaps), the "Gorilla" authors prefer using logical reasoning.

And "The Invisible Gorilla" stands out in at least one way: Its authors actually do scientific research. The book's title comes from an experiment they did more than a decade ago.

They showed subjects a video of people passing a basketball and told the viewers to count passes between the people wearing white. A person in a gorilla costume walked through the basketball scene during the video.

After the video, the subjects were asked about the passes. Then they were asked whether they saw anything unusual. They even were asked point-blank whether they saw the gorilla. About half of the people did not see the gorilla, exhibiting "inattentional blindness." Some could not believe they missed the gorilla until they watched the video again. It was an irrefutable lesson that the mind, not to mention confidence, can be misleading.

"It's rare that you get feedback that you're wrong," Simons says.

So "The Invisible Gorilla" gives us, in a nice way, that feedback.

Here are some more things that you (or people you know) might be wrong about:

• Listening to classical music makes you smart in other areas. (It doesn't.)

• Brain games make you smarter. (Playing Sudoku makes you smarter only at Sudoku or a game very similar.)

• You're smarter than average. (71 percent of men think they are smarter than the average person.)

• You can multitask. (Doing two things at once means you are paying less attention to each. Talking on a cell phone while driving is probably even more dangerous than you think.)

• You're good at investing. (You're probably worse at picking stocks than a professional investor.)

Simons doesn't want readers to feel utterly discouraged. But his book says paying attention and being skeptical of everyday assumptions might lead to better driving — or even derail the next seductive Ponzi scheme.