Quoting Paul Graham:

The number one thing not to do is other things. If you find yourself saying a sentence that ends with "but we’re going to keep working on the startup," you are in big trouble. Bob’s going to grad school, but we’re going to keep working on the startup. We’re moving back to Minnesota, but we’re going to keep working on the startup. We’re taking on some consulting projects, but we’re going to keep working on the startup. You may as well just translate these to "we’re giving up on the startup, but we’re not willing to admit that to ourselves," because that’s what it means most of the time. A startup is so hard that working on it can’t be preceded by "but."