When I was green, young user, I entrusted some HYIP project with my BTC in hopes to get easy and fast profit.
Soon, all "invested" Satoshis were lost (obviously). And I learned from this stupid mistake.
I think from all the replies that most of the users have lost their bitcoins in hyips and gambling.
But if you see these are not actually losses but its a loss made while trying to earn, or call it a part of learning, so yeah nice to know you learned something new from your own mistakes.