diff --git a/src/content/posts/reading-notes-predictably-irrational/index.md b/src/content/posts/reading-notes-predictably-irrational/index.md
index 6251820d0..8f396027a 100644
--- a/src/content/posts/reading-notes-predictably-irrational/index.md
+++ b/src/content/posts/reading-notes-predictably-irrational/index.md
@@ -39,5 +39,11 @@ Ch. 2 - Anchoring Effect
 Ch. 3 - 抽卡定律：首抽免费
 --------------------------
 
+Ch. 4 - Social Norms v.s. Market Norms
+--------------------------------------
 
+We live simultaneously in two different worlds
+
+1. one where social norms prevail, and 
+2. the other where market norms make the rules.