[stcredzero]

> If a user can't figure out how to navigate through an app in a reasonable amount of time without a great deal of existing knowledge

Having watched kids, teens, and 20-somethings, I've concluded that "a reasonable amount of time" to them is something on the order of 5 seconds on the outside. On a PC, they might look around and thoughtfully click on things. On a tablet or phone app, they just mash their fingers for about 3 seconds, then if they haven't seen something, move on.

This even extends to 20-somethings and game controllers. I've seen 20-somethings walk up to an 80's emulated arcade game, waggle the sticks on a controller for 2 seconds, not understand why the screen was shaking, then walk away.