The first illusion is that we don't notice the unexpected -the invisible gorilla of the title- we see what we expect to see. Sometimes we don't see the wood for the trees -an innocent man was found guilty of rape because the victim concentrated too hard on remembering different aspects of his features.
The second illusion is that our memory is accurate. I know from experience that mine isn't. A simple example is watching a film you enjoyed for a second time and realising how much you have misremembered about it. The illusion of memory explains why several people can give completely different accounts of the same incident.
This is just the beginning of it but I won't go into any more because I really want you discover the contents of this fascinating book for yourself. Ironically it confirms many things that I've already thought of and it isn't because I'm a clever clogs. It's because I know I have a poor memory, because I know I'm not as clever as I'd like to be, because I know I'm not an observant person, and, unless I'm dealing with something I do know well, I'm not a confident one. To understand that statement you really do need to read this book. You'll see yourself and the world around you in a new light. That's a promise.