In 2010, you came across a site that was giving away bitcoins. The site said it was free money so you signed up. You were logging in to figure out how it was money but couldn't. The last time you logged in you had more than 100 bitcoins. Later you forgot about the site until 2017 when a ponzi was advertising Bitcoin. Bitcoin? The name rang a bell and you stated hearing stories. You remembered you must have many bitcoins somewhere but you can't even remember the name of the site. How would you recover your BTC?
I think its impossible to recover that because you don't even know what the site is. Or maybe for a long time you forgot also your email there i think you can not recover it. You need first remember what site it is and the second one remember what email you used when signing up there and if the email are active.
If you remember all that you can easily recover that bitcoin but once you forget one of then i told you its not easy to recover it.