Generally, you won't lose money. There was a scam site called dicebitco.in, and they scammed house's 500 btc fund with cheating. So you need to invest on reliable site.
It's a theory, that the highly profitable investment or double the money and would not eliminate the money. That is certainly true, but if we are not smart in choosing investment then something negative things will happen to you in the future, as you say friends. That investment must be in need of a clear track record, so that we do not become a victim of fraud