Nothing ever is, but is always becoming.
– Plato, Theaetetus

As requirements mature and products evolve, it can be tempting to heap features and functionality onto the surface: pick a position in a navigation scheme and insert a menu item; find a free spot on a screen and stick a button on it; the story’s in the backlog, so slap on a UI control and call it a day.

The append-a-feature approach is like a throw-on-whatever-topping pizza party: both generate mixed results and both went out with the 90s. Sure, a successful product or pizza experience may emerge by coincidence, but append-a-feature is interaction roulette not interaction design.

Interaction design helps people live their lives by presenting options that cohere with their situation. It avoids bombarding people functionality that they’ll only need until later. Drawing on the principle of staged disclosure, an inspiring example of just-in-time interaction: