Both of this (Lost and Stolen) happened to me. Actually at the beginning it's common to make a mistake but if it happens several times like me than it's a worst thing.

My purpose to share my stories so that newbies can learn from it and never do like this. First I have lost some of my Bitcoin by sending it to a wrong wallet address. I sent in a hurry and lost it because the destination address was wrong. Then I also sent my BTC to another Blockchain but all the mistakes I have done all are in a hurry. So my advice is that " Never be Hurry when you are making any transection and always recheck your wallet address and the Blockchain

And I have been scammed by a person when I didn't use an escrow and sent it first. They as usually he blocked me though he was much trusted to me but a unknown person. So Always use an escrow you you want to deal with someone you don't know perfectly.