Facebook users are always concerned that they will get locked out of their account.
Facebook has a security measure where you can designate three trusted contacts for password recovery.
So how does it work ?
Say you forget your Facebook password, Facebook will send each of your 3 designated friends a code, then you’ll need to get all three codes to get back into your account.
The good thing about this is that without the 3 pieces you cannot get into your account that is why they send only 1 piece to each friend.
More information can be found here :How can I choose friends to help me log in if I ever get locked out of my account?