So this thread is one of my most successful one at Bitcointalk with over a hundred pages or replies. Anyway, first edit to the first post was made.
Listed down some common mistakes people made with Bitcoin.
1. Gambling.
2. Not knowing Bitcoin earlier.
3. Participating in HYIP & Wrong trading technique (both Altcoin and day trading).
4. Sending to wrong address & lost of wallet.
5. Cloud mining & scammed trade.