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.
Since i don't gamble no 1 doesn't apply to me. But no 2-4 are things i recognize. If I could do it all over I would have saved at least 4-5 bitcoins.
For me was learning money...
Good to know that you do not gamble! If you do gamble and become addicted to it, you would have lose more than what you lost from point two to four. Anyway, spending 4-5 Bitcoin learning about money ... is a somewhat good investment.
Sending to wrong address
Can't we put all errors listed in this thread into this single category?

I sent my coins to the wrong investments... I should have send it to another address of mine instead.

Haha. This is actually the fourth most mistakes I read so far. I have never send to a wrong address before because I will check whenever I send Bitcoin - even if I copied and paste or used QR code.

I did not any mistake
I think I am on right way
Good to know that. Welcome to the crypto world and do not make any mistake at all - especially getting into gambling or HYIP.