People assume summarising is about compression — squeeze the book until it is small. It is not, really. Compression keeps everything and makes it tighter. Summarising is something harder and more opinionated: it decides what to remove entirely, and lives with the consequences.
Every nonfiction book is a mix of two things. There is the load-bearing structure — the handful of ideas the whole book rests on, the moves you will actually use. And there is the scaffolding — the anecdotes that warm up each chapter, the third example proving a point the first two already made, the throat-clearing that gets an author from one idea to the next. The scaffolding is not bad. It does real work while you are reading. But it is not what you came for, and it is not what you keep.
What is load-bearing
The test we use is simple to state and hard to apply: if we removed this, would the argument still stand? If the book still makes its case without a passage, that passage is scaffolding, however charming. If the case falls down without it, it stays. Most of a book turns out to be scaffolding. That is not a criticism of books; it is what makes them readable. It is also what makes a faithful summary possible.
The art is not in what you keep. Anyone can keep things. The art is in what you can bear to cut.
Faithful, not shorter
The line we will not cross is the idea itself. A summary that drops a load-bearing point to save a minute is not shorter — it is wrong, and quietly so, because the reader cannot see what is missing. So we cut examples, repetition, and tangents, and we guard the argument with everything we have. Read one of our gists and then the book, and you should recognise every essential beat. You will simply have met them without the scaffolding.
Leaving things out is the whole job. Done carelessly it produces a thinner, dumber book. Done well it produces the same book, honestly, in a fraction of the time — which is the only version of brevity worth trusting.