There's actually 52 cards that compose the Book of Sorrow. There's are 50 calcified fragments total though. Upon getting your first fragment you get the card "Calcified Fragment: Curiosity" in addition to the card for whatever fragment you picked up. Upon getting the final fragment you also unlock "Calcified Fragment: Insight."

Its either you have to have all fifty or complete oryx challenge on hardmode I do know around December players report that insight card was bugged The bug could still be existent to some players I know when I got all fifty fragments insight pop up after my final fragment- oryx challenge but I did it on hardmode Okay I looked at your profile You're missing the gor challenge https://youtu.be/2qzZ-qXa8L8 You only get insight if you have all fifty fragments The fragments as said many times by bungie its account wide not character Thats why its important to have a main character to do all the important content- such as collecting fragments You can do the normal raid gor challenge to get the fragment- http://www.usgamer.net/articles/destiny-kings-fall-raid-challenge-mode-guide Good luck