If you had to guess, is it just that second-time founders have more experience, or is it that a lot of the first-time founders who aren't 'cut out' for startups try once and then give up? (Honest question!)
It would be hard not to get better at being an entrepreneur through the practice of starting a company and failing. There's no shame in failing at something that's really hard to begin with, so long as you learn a lot and act with integrity.