"Many did not notice [the fight]," Chabris said. "The thing you think is salient -- people fighting -- should grab your attention, but if you're chasing a suspect it's shockingly easy to miss things that in retrospect seem obvious."
So, padlocks on doors in a grimy house? It's entirely plausible that a neighbor going to borrow an egg, for instance, wouldn't see them.
"You're not going over there with the task of looking for something unusual," Chabris said.
Our brains form fast, general categorizations of our surroundings, said Barbara Tversky, a psychology professor at Teachers College, Columbia University.
"The world is terribly confusing; there's too much happening at the same time -- visually, auditorily, everything -- and the way we cope is by categorizing," she said. "We process the minimum we need in order to behave properly. Things that are aberrant blend in."
Plus, humans are able to focus inwardly while performing outward tasks, such as walking to the grocery store.
"We can walk down the street and think about a grocery list," she said. "Our minds are interested in more interesting things than just walking around the world. We aren't aware of how much we're missing."