That only works if icons remain consistent and reasonably detailed over long periods of time. Nowadays all icons are abstract, monochrome shapes. They are similar enough to each other, and vary enough from one application to another, that one application's "back" or "new" buttons can look pretty similar to another's "undo" or "copy" buttons. With most apps on my phone I have no idea what the buttons do unless I press them, even if I'm perfectly familiar with the function.