To grow rapidly, you need to make something you can sell to a big market. That’s the difference between Google and a barbershop. A barbershop doesn’t scale.
For a company to grow really big, it must (a) make something lots of people want, and (b) reach and serve all those people. Barbershops are doing fine in the (a) department. Almost everyone needs their hair cut. The problem for a barbershop, as for any retail establishment, is (b). A barbershop serves customers in person, and few will travel far for a haircut. And even if they did the barbershop couldn’t accomodate them.
Writing software is a great way to solve (b), but you can still end up constrained in (a). If you write software to teach Tibetan to Hungarian speakers, you’ll be able to reach most of the people who want it, but there won’t be many of them. If you make software to teach English to Chinese speakers, however, you’re in startup territory.
Most businesses are tightly constrained in (a) or (b). The distinctive feature of successful startups is that they’re not.
Long and thorough post, worth your time if you want to start a startup.