What he meant by "thin books" is pretty obvious: a thin book is a book in which a simple idea is presented without fluff, delivering value without noise. Lately I started reading more, and I found myself skipping pages and getting somewhat frustrated when the author spends too much time reiterating on the same concept over and over, likely in an attempt to increase the page count. Sure, some topics require more pages, but that is not always the case. I am sure we can all relate to that, and I won't spend much time on this part.
The second part of that sentence is much more interesting: a "quick silence". Shaan explains this saying that when he has a business question he calls one of his friends and asks him the question - whatever that is. Then: "There's a quick silence. He says his thing, it's obvious, that's the answer."
Have you ever asked a question and then realised that you kinda knew the answer, all you needed was somebody else to say it for you? Or, on the opposite end, have you ever asked a question and then dived down into a never ending chain of if-else scenarios that are not relevant at all unless you do something to get data to even know if these scenarios are likely?
I know I have done both.
Hearing him say that made me stop and think. Sometimes you know you are asking the right question when you get either a thin book or a quick silence. When you have too many questions that could be a symptom of the fact that you are asking the wrong ones. Time to take a step back and figure out what you need to ask instead - and if you realise that you know the answer, sure you can ask for confirmation. But sometimes it's easier and faster to simply go and do the thing.