There are 32 coffee mugs in the image below, but did you notice that one of the coffee drinkers is a gorilla? If not, blame inattentional blindness. As it turns out, your mind is capable of making unexpected objects invisible right before your very eyes.
Also called the "monkey business illusion," inattentional blindness refers to our inability to see objects if they're not the primary focus of our attention. According to a 2012 Smithsonian Magazine article by Experimental Psychologist Daniel Simons, "We consciously see only a small subset of our visual world, and when our attention is focused on one thing, we fail to notice other, unexpected things around us—including those we might want to see."