Your brain fails to focus on details all the time.
Change blindness allows the brain to focus on one precise thing and that's very useful and a great survival mechanism. But since most of the time we're not aware of what the brain focuses on, we cannot have a full picture of our daily lives; it distorts our perception constantly.
This concept explained and much more in the documentary series "Brain Story" (2000) by the extraordinary British Broadcasting Corporation (BBC). http://www.bbc.co.uk
Full description of the original documentary series: