Actually startups take off because the founders make them take off. There may be a handful that just grew by themselves, but usually it takes some sort of push to get them going. A good metaphor would be the cranks that car engines had before they got electric starters. Once the engine was going, it would keep going, but there was a separate and laborious process to get it going.
The most common unscalable thing founders have to do at the start is to recruit users manually. Nearly all startups have to. You can’t wait for users to come to you. You have to go out and get them.
At YC we use the term “Collison installation” for the technique they invented. More diffident founders ask “Will you try our beta?” and if the answer is yes, they say “Great, we’ll send you a link.” But the Collison brothers weren’t going to wait. When anyone agreed to try Stripe they’d say “Right then, give me your laptop” and set them up on the spot.
There are two reasons founders resist going out and recruiting users individually. One is a combination of shyness and laziness. They’d rather sit at home writing code than go out and talk to a bunch of strangers and probably be rejected by most of them. But for a startup to succeed, at least one founder (usually the CEO) will have to spend a lot of time on sales and marketing. 
The mistake they make is to underestimate the power of compound growth. We encourage every startup to measure their progress by weekly growth rate. If you have 100 users, you need to get 10 more next week to grow 10% a week. And while 110 may not seem much better than 100, if you keep growing at 10% a week you’ll be surprised how big the numbers get. After a year you’ll have 14,000 users, and after 2 years you’ll have 2 million.
But if the market exists you can usually start by recruiting users manually and then gradually switch to less manual methods. 
Airbnb now seems like an unstoppable juggernaut, but early on it was so fragile that about 30 days of going out and engaging in person with users made the difference between success and failure.
It’s harmless if reporters and know-it-alls dismiss your startup. They always get things wrong. It’s even ok if investors dismiss your startup; they’ll change their minds when they see growth. The big danger is that you’ll dismiss your startup yourself. I’ve seen it happen. I often have to encourage founders who don’t see the full potential of what they’re building. Even Bill Gates made that mistake. He returned to Harvard for the fall semester after starting Microsoft. He didn’t stay long, but he wouldn’t have returned at all if he’d realized Microsoft was going to be even a fraction of the size it turned out to be. 
Not very userful to see lots of tech news and reports
The question to ask about an early stage startup is not “is this company taking over the world?” but “how big could this company get if the founders did the right things?” And the right things often seem both laborious and inconsequential at the time. Microsoft can’t have seemed very impressive when it was just a couple guys in Albuquerque writing Basic interpreters for a market of a few thousand hobbyists (as they were then called), but in retrospect that was the optimal path to dominating microcomputer software. And I know Brian Chesky and Joe Gebbia didn’t feel like they were en route to the big time as they were taking “professional” photos of their first hosts’ apartments. They were just trying to survive. But in retrospect that too was the optimal path to dominating a big market.
Small and Big
Why do we have to teach startups this? Why is it counterintuitive for founders? Three reasons, I think.
One is that a lot of of startup founders are trained as engineers, and customer service is not part of the training of engineers. You’re supposed to build things that are robust and elegant, not be slavishly attentive to individual users like some kind of salesperson. Ironically, part of the reason engineering is traditionally averse to handholding is that its traditions date from a time when engineers were less powerful—when they were only in charge of their narrow domain of building things, rather than running the whole show. You can be ornery when you’re Scotty, but not when you’re Kirk.
Another reason founders don’t focus enough on individual customers is that they worry it won’t scale.
But perhaps the biggest thing preventing founders from realizing how attentive they could be to their users is that they’ve never experienced such attention themselves.
Tim Cook doesn’t send you a hand-written note after you buy a laptop. He can’t. But you can. That’s one advantage of being small: you can provide a level of service no big company can. 
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