Researchers have now tried to explain why we sometimes miss what is right in front of our eyes- they have called it "inattention blindness".
This is perhaps what causes many of us to miss the traffic lights while we are talking away on the phone.
Research says that those who fail to see something right in front of them while they are focusing on something else actually have reduced "working memory capacity".
Study co-author, Janelle Seegmiller, psychology doctoral student at the University of Utah in the US said, "Because people are different in how well they can focus their attention, this may influence whether you'll see something you're not expecting."
To demonstrate this condition, researchers used a video showing six actors playing basket ball. Viewers were asked to count the number of passes made by the players. People were so engrossed that they did not notice a person conspicuously dressed in a gorilla suit thumping his chest amid players on the field and walking off.
"We found that people who notice the gorilla are better able to focus attention," says Watson, also an assistant investigator with the university's Brain Institute.
"You can imagine that if you're driving and road conditions aren't very good, unexpected things can happen, and individuals with better control over attention would be more likely to notice those unexpected events," Seegmiller says.