No matter how highly trained or how dedicated a human observer, it is impossible to provide full attention to more than one or two things at a time; and even then, only for a few minutes at a time. A Harvard University study concluded that humans are surprisingly unaware of the details of their environment, and often do not detect large changes to objects or scenes ('change blindness'). The Harvard experiment results showed that 50% of people counting the passes made between two basketball teams will not notice a gorilla walk into the middle of the viewing area, beat its chest, and walk out. The conclusion is clear- humans do not reliably detect security threats, whether watching live video or viewing archived data, resulting in false conclusions that nothing occurred when, in fact, something did (referred to as 'false negatives').