I learned to type in high school on manual typewriters (yes, they were outdated even then!). Typing on an IBM Selectric typewriter was a whole lot easier, but it took some time to adjust the force of my typing — the electric typewriter required a lot less force to activate. This made typing easier, but, in an odd way, also less satisfying. Pressing “Enter” is not as gratifying as slamming the carriage return back over.Of course, if you slam the keys of an electric typewriter, you’ll break them. So you learn to type more lightly, and is uses less energy, and it’s easier. But less fun.Not long after, we moved to computers. 386-processor IBMs and a Mac Quadra 700 running the brand-spanking-new OS 7 (boy, am I dating myself in this post). These were so much easier to type on than the IBM Selectric. They required much less force on the keys… it was easier, but took some getting used to. The MacBook I bought last month demands a lot less finger power than the PowerBook it replaces. And on and on.Were I to type on my MacBook with the force I used on a Quadra 700 — let alone an electric or manual typewriter — I’d destroy the keyboard in days, if not hours. So I learn to use a lighter touch. And my interaction is less visceral as a result. Still, there is a very tangible physical contact between my fingers and the keys which provides constant feedback and response.Nintendo Wii has been a huge success, and it’s not just because it costs less than Sony Playstation and Microsoft XBox. Using the motion-sensing remote control creates an immersive, physical, visceral experience… in other words, it’s fun.The iPhone has set the mobile world on its ear by making interaction with the phone fun (see my earlier comments here). Using a touch screen has lots of usability advantages, but what makes iPhone stand out from the rest of the touch screen crowd is the visceral, physical sense of direct interaction with the data and lists. It’s fun.Competing manufacturer response has been (duh!) to start making more smartphones with touch screens. Bigger touchscreens, faster touchscreens, projective touchscreens. Which misses the point. In fact, it may do worse than miss the point… When you move to a more sensitive input method (for example, a more sensitive touch screen, or a screen that can sense your input even before you touch it, or voice activation, or camera-based gesture recognition), you don’t have to use as much pressure to activate the device. In other words, you need less physical interaction, and less intentional activation to generate a response.Sarah’s rule states:

More sensitive device input [device sensing] + more sensitive devices [device fragility] = lighter, less visceral contact/interaction. 

Do you want to create a product that makes people want to spend time with it? Follow Nintendo’s lead, and give it some real physical interaction. The more visceral, the more engaging. You’ve been warned.