Like many others, I’m spending more and more time on my phone, and I’m not making more calls.  I’m getting information, buying stuff, collaborating with others and much more.  There are a handful of mobile apps that I use religiously to do these things.  Why do I use these specific apps as regularly as I do?  I suspect that the answer for me and for many others who have the same behavior (a few select apps used frequently) boils down to a few simple things.

Scale is the outgrowth of doing just one thing really well.  WhatsApp, Instagram and Shazam are great examples of products and companies that expertly address a single, well-defined need in a simple way that satisfies a large number of people.  They haven’t added tons of new features to address additional use cases or at least they didn’t begin to do that until they had already significant user scale.  A single-purpose app makes it easier for a user to remember why she should use that app at the moment that she has a specific need.

Users inherently have a tendency towards mental inertia.  Once a user begins thinking of an app as addressing a particular need, it’s really hard to get him to think about it or use it differently.  An app developer who adds lots of features to an app risks confusing users and detracting from the core use case that the app is meant to address.  Unlike the desktop web, where tabs, menus, filters, etc. can be used to add features, it’s likely that in the mobile world the only successful way to add features will be to build entirely separate apps (see Twitter’s Vine and Facebook’s Messenger), often under separate brands.  Can you think of a single app that you use that does many different things well?

Better isn’t good enough.  Once a user begins to think of an app as addressing a need well, it’s really hard to get him to switch to another app to address the same need, even if it does it “better” (see Facebook’s Poke vs. SnapChat).  It’s not enough to be better in mobile, you need to be first to get to scale or you need to be different to fight inertia (not to mention switching costs, network effects, etc.).  WhatsApp continues to thrive in the face of increasing competition because it was first to address a specific need well.  SnapChat and Instagram succeeded not only because they did only one thing extremely well, but also because they did something different from Facebook and Twitter.  They addressed entirely new use cases and didn’t settle for competing via marginal feature innovation (which seems often to be the case in the messaging category, as one example).

Great products unlock user acquisition.  How did Uber grow virally?  The challenges of mobile app discovery and distribution have been well documented. App store distribution, pay-per-install ads, incentivized referral programs, etc. all face obstacles in mobile.  If you don’t have a product that requires users to invite others to benefit from the app (i.e., Facebook), there is only one true answer to the distribution problem.  The best distribution strategy is to build a killer product that generates tremendous word-of-mouth.  Uber, HotelTonight and Mailbox are examples of mobile apps that delivered amazing user experiences that in turn led to viral growth via word-of-mouth.  More than ever before, being the first to deliver an elegant solution to a user problem can be the key to dominating distribution and hence an entire market.

Surprisingly, when I thought about the points above, it seemed that what is true in mobile has largely been true on the web as well.  While technology changes, human behavior is pretty ingrained.  The mind craves simplicity and consistency and resists complexity and change.  Mobile app developers who want to achieve scale will be well served by satisfying the mind.