1. You assume because a "korean immigrant" can do something, that it must not be intractable (hard). Immigrant entrepreneurs are usually highly motivated, especially the kind who start small businesses. I would rescind that comment.
2. You are comparing a dry cleaner to a startup. The failure rate of startups is several order of magnitudes worse than a dry cleaner. Figuring out the potential numbers for a dry cleaner is simple math that you can base on the local population, income/employment stats, and # of dry cleaners. Most startups would kill for that kind of estimate.