If we're concentrating on something in particular, our brains skim over the rest of the details and fill bits in for the other places we're not looking at directly, so it's surprisingly easy to completely fail to notice something really obvious that's right in front of your nose. It's an interesting effect but it's not very flattering about our ability to multitask :/
Lynx is describing the invisible gorilla effect. http://www.livescience.com/6727-invisible-gorilla-test-shows-notice.html
If we're concentrating on something in particular, our brains skim over the rest of the details and fill bits in for the other places we're not looking at directly, so it's surprisingly easy to completely fail to notice something really obvious that's right in front of your nose. It's an interesting effect but it's not very flattering about our ability to multitask :/