I used to think I was a complete fool. However, as I've gotten older I've come to realize that thankfully I'm not alone. I would have such difficulty with everyday products (scissors that don't cut, food products that can't be opened without scissors, shampoos that can't be opened with wet hands etc.) that I figured, what's wrong with me? Now I know that these products are actually in many cases badly designed. Don Norman's The Design of Everyday Things helped me understand that.
Norman walks the reader through all the things one must think about when designing a product. How people think and how people actually use the product, rather than how the products' designers think, are the important things here. Norman delves deeply into these topics to make sure the reader has a complete view of what he should be doing when designing a product.
The book is not as practical as I would have liked, however. It doesn't say "Do it like this", but rather "You can figure out how to do it by thinking about these aspects". Also, though there are some exceptions in part as the book has clearly been updated recently, the thinking seems really geared to hard products rather than software, which is the area that interests me more.
If anyone works on designing, manufacturing or marketing any type of physical product, I think this is a must read.