It makes sense to me... if everyone has told you to get book x then you assume it’s because it’s the best, and therefore in one case you know what the best book

It makes sense to me... if everyone has told you to get book x then you assume it’s because it’s the best, and therefore in one case you know what the best book is... E.g. when learning ruby many people recommend the pickaxe book. You could safely assume it’s because it’s the best reference guide to ruby, therefore making it an easy decision to get.