How to find insights of a book summary?

Insight — is key information in every summary chapter, shortened to one sentence. You can add these quotes to your Repetition cards or access them when necessary.  Even if you finished the book a long time ago, it is always possible to refresh essential notes in the Insights section. 

To do that, open the book you like and tap the 'Read' button. After that, open the menu on the upper right corner of your screen, as shown in the screenshot:

Then, switch to the "Insights" tab.