The two year crisis

I'm having a crisis about my novel. I've been writing it for two years and I suddenly realise that large parts of what I've written are entirely off the point and need to be scrapped. I don't feel good about this. Except that I've been through this with three novels before. It always seems to happen. When I'm two years in I always realise that the book isn't about what I thought it was about. It's depressing but perhaps it is just part of the process - or my process, at least. And the main thing I've learnt about writing is - DON'T ARGUE WITH THE PROCESS. Arguing with the process wastes time and gets you nowhere. So I'll just keep going and hope that it comes right. I think that it will do but I get bored of waiting.