Well, then you fail.
But let me tell you - as someone who has 'failed' multiple times - two things:
1. You will not fail, even if every cell in your body and mind may think otherwise at some point, and,
2. The words 'fail' our 'failure' are only labels that you paste onto yourself in your own head.
Look at your fear of failure with a bit of distance and you'll begin to see that you can't really fail. You will have tried and maybe not reached your intended goal, but you won't fail or be a failure as there are so many other and unpredictable outcomes of your adventure.
When I look back on my own fears of failure (and notice the plural of fear I am using, that is how bad it was!) I think the main one I had is that I would let others down; that I jumped into this glistening and sparkling pool of ambition, enthusiasm and energy, and that I may not even make it to the other end.
So please believe me when I tell you it makes no sense whatsoever to spend any time or energy thinking about failure in whatever form. Don't go there. I did, and for years I felt like I was traipsing through a desert with a bag of sand thrown over my shoulder, and I kept looking for the most perfect place to empty this bag. But of course there was no perfect place; all I did was spend energy and time lugging this silly bag around, feeling like a failure and beating myself up about it, instead of seeing the valuable things I learned and applying these to new and future ideas ventures. So, drop the bag, turn around and forget about failure because the only place it exists is in your mind.