This book is popular among the software developer crowd (think the UX version of Lean Startup).
The premise of this book is that many things are designed poorly for the end-user.
This bit, 'for the end-user', is important. Why?
Many of the things designed poorly for the end-user are also:
These good qualities (fine-wrought, expensive) mask an important bad quality: they actually suck to use for the people who will actually be using them.
Norman's antidote to this is 'human-centered design', which more or less amounts to 'do not make your product suck to use'.
'Design of Everyday Things' is not well written and is unenjoyable to read. It falls into the category of a Blinkist book, that is, a book with 15 minutes of ideas spread across 200 pages of bad writing.
Norman unhelpfully invents his own vocabulary:
"I call the signalling component of affordances signifiers" 
"I call the combined information available to us the system image" 
Norman offers some rules of thumb for designers:
These rules seem pretty well understood, even by non-UX people. The big ideas of DoET are gospel in 2018. Should you even bother reading the book?
I'd argue 'yes'. Given how often we make UX mistakes, and how little devlopers seem to care about providing a good experience to other developers, reading Norman is like reading reading Dale Carnegie's 'How to Win Friends and Influence People'. The message isn't new but bears repeating, at least until we start getting it right.