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.
It may not scale, but the chances of it making (any/more) money are much higher ("riches are in the niches") than a "fast startup" as it's very rare for a startup to grow fast and monetize quickly at the same time, because most people just won't buy immediately, sometimes even if it solves a problem for them.
For example, I've been using Evernote and Dropbox for years, but haven't had the need to buy a premium account. I believe there are many others like me who are happy with the free (or open source) software that does solve an itch. Are these "fast startups"? Is their business model (freemium) scalable?