Ask HN: Experiences running a small business vs. a startup?

Please forgive my naïveté, I would like to understand the commonalities/differences of running a small business vs. a startup. I see that both have to deal with finances (loans, investors), developing a product, marketing, transaction processing, labor (employees, contractors), and taxes/accounting. What are the experiences, motivations, and day-day like with respect to small business vs. startups? I've heard others talk about small businesses and startups as distinctly separate types of business, but I'm still confused why they are so different?