diff --git a/README.md b/README.md
index a21cc93..59832d8 100644
--- a/README.md
+++ b/README.md
@@ -1,6 +1,5 @@
 # go-lottery-generator
 
-
 A lottery number generator written in Go that generates random sequences and tracks when any sequence appears multiple times.
 
 ## Features
@@ -24,6 +23,12 @@ go run main.go
 Done
 ```
 
+## Why "stop at 6 appearances"
+
+This is a statistical curiosity inspired by [Vietlott](https://vietlott.vn/) Power 6/45 — Vietnam's national lottery where players pick 6 numbers from 1–45. The question: *how many draws would it take before any exact 6-number combination repeats?*
+
+By the birthday paradox, with C(45,6) = 8,145,060 possible combinations, you'd expect a repeat after roughly √(2 × 8,145,060 × ln 2) ≈ **3,360 draws** on average. This program runs the simulation and stops as soon as one sequence has been generated exactly 6 times — letting you observe the actual count empirically.
+
 ## Original Python Version
 
-*In 2025, I rewrote this project using Go. The original Python version of this project can be found at [feature/python](https://github.com/tiennm99/lottery-generator/tree/feature/python) branch.*
\ No newline at end of file
+*In 2025, I rewrote this project using Go. The original Python version of this project can be found at [feature/python](https://github.com/tiennm99/lottery-generator/tree/feature/python) branch.*