Inattentional blindness can be understood as the failure to see events when one is paying close attention to another event. It is being so completely absorbed in one task, that you completely overlook (or do not see) other things around you. Studies have shown that when a person is attending to one task, he or she can completely miss anything that is unrelated to the task. It sounds unbelievable, but I'm not talking about not noticing simple things or things that are "easy" to miss. I'm talking about things as ridiculous as not noticing a person in a gorilla suit dancing through a frame or a clown riding a unicycle right past them. In the clown experiment, participants were talking on their cell phones and did not notice a clown riding a unicycle past them! Now, you might be thinking, "These are just experiments. A clown? On a unicycle? I would notice something like that!" But, real people, just like you, in the real world are easily distracted.
In the real world, inattentional blindness is known as multi-tasking. And in the real world, there can be dangerous consequences. Recently, two pilots flying a Northwest airplane overshot their destination, Minneapolis, by 150 miles! They weren't on Facebook or Twitter or reading the newspaper. They were multi-tasking. The pilots claim they were trying to figure out their company's new flight crew scheduling system. While flying the plane. And they simply forgot to land! And they did not hear their cockpit instruments beeping at them or the calls from air traffic control. Fortunately, there was a happy ending and this is just a cautionary tale. Unfortunately, too many people think they can multi-task. Many people use their cell phones while driving. According to a recent study, 28% of car accidents involve people using their cell phones while driving.
All of this is to say that we should be aware of the possibility of inattentional blindness. It's okay to not be able to do two (or more) things at once. It's in our wiring.