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 have also had this same fears sometime back and hence i decided to write out all my account usernames, emails and their respective passwords. I have backed this up in several other books as well and stored them somewhere very safe. You have to go the length and breadth just to keep those funds. I know so many people are cursing their stars as to the number of bitcoins they don't have private keys to.