I don't think the problem is the action of selling and starting anew. I think the problem is double-talk. Either treat your startup like it's your life's work

I don't think the problem is the action of selling and starting anew. I think the problem is double-talk. Either treat your startup like it's your life's work and see it through for as long as it takes, or treat it like a big project that you're happy to turn over when something better comes along. But keep the attitudes distinct.