Everyone has one and every writer should have two. All the things I've written that go nowhere often help me climb otherwise impossible creative obstacles when reviewed. Hindsight is twenty-twenty when it comes to creative things. There are so many things you can do right in the present if you knew what you did wrong in the past.
Make sure you keep what you did in the past, no matter how terrible or malformed.
(Edit: It occurs to me there's two ways to read that last sentence, comma arrangement notwithstanding, both work...)