How do you decide whether the features in your product are enough to launch?

It's often a constant struggle to reach a conclusion on what the minimum viable version of the product should be, especially when you feel intimidated by the awesome features and capabilities that other similar products might already be having. Just, as you fine-tune things, you may figure out there is some extra feature that you think will help you shine above your competition, or will make your product a bit more useful. How do you prevent over-optimization or premature-optimization? When you already have a big enough userbase, you can always ask them but, how do you handle this issue when you are just starting out.