You are looking for the brand new, next big think, and you keep throwing the paper in the bin. Whereas, if you start off with the local cleaner who shit himself at work and got sacked, at least it's a starting point. I think the secret to making an original film is just having something you can work on. Not trying to think of something that isn't you. Anything that actually succeeds is only deemed original when it actually comes out.
Most successful writers come about through writing that life long project.
Trying to write something original is a means to an end. What I do is write something I care about and worry about whether people think it's original later. What I do, is go away and write for two weeks and have a really condense period to write a draft. I won't have loads of months writing. Then I come up and get a group of actors together who I think will hopefully be right for the part.