Cedric Chin writes about the development of the original iPhone’s keyboard:
Nobody on the 15-engineer team quite knew what the ideal software keyboard would look like. Over the next few weeks, the engineers developed a wide variety of prototypes. One developed a Morse-code-inspired keyboard which would have the user combine taps and slides to mimic dots and dashes. Another developed a piano-like keyboard where users would need to click multiple keys at once (hence the name) to type a specific letter. The remaining prototypes downsized the usual QWERTY keyboard, but these came with their own set of problems. The buttons were too small and there was no tactile feedback to tell the user whether they had hit or missed the button.
This is a great illustration of how the most obvious solution, in hindsight, is often not at all clear in the moment.