Seth Godin says, Square one is underrated. I agree, kind of – but I think there’s actually no such thing as “going back to square one”.
If your project is going in the wrong direction, you can go back and start over, but at this point you’re not really at square one – hopefully you know where you went before, you remember most of the decisions (good or bad) that you made, and what their consequences were. You’ll do better because you’ll benefit from your own experience.
Think of it this way – even if you throw away everything you’ve written so far, you haven’t thrown away all that time and work you put into it – as long as you don’t take too long to get back into it, you’ll soon be ahead again.