My book is #$%^&*

Does anyone have days when they're just writing away, doing their best to write a decent story and then they stop and just think, oh my goodness. My book sucks.

At the moment i'm plugging away, writing my heart out and just letting the story flow from my fingertips. But then I stop. It's almost like i'm building a wall for myself that I just can't get past. I'm building it on purpose. My story is crap. The dialogue isn't flowing as naturally as it should.... it just doesn't feel natural. It feels too forced.

Then of course I go on a whirlwind of self-doubt and wonder if I'm really cut out for this particular path or not. Could I even manage to get this book finished if I can't get through a chapter without criticising my work? My mum's always said i'm my own biggest critic. I know that, but I also know when I can do better... and this... it's not better.

How do you get past this? Are first drafts usually this awful? Does most of the 'decent' writing come in the editing phase? It's so hard to get past the self-doubt and criticisim.

So many times I just wanna delete it all and start over. But that'd just be a waste of time now, wouldn't it! What are your experiences?