I'm James Hague, a recovering programmer who has been designing video games since the 1980s. This is Why You Spent All that Time Learning to Program and The Pure Tech Side is the Dark Side are good places to start.
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Are You Sure?
It's an old, familiar prompt. You delete a file, discard a work in progress, or hit Cancel mid-install:
It's not always so quaintly phrased these days, but the same cautious attitude lives on in the modern confirmation box. In iOS 8, tapping the trash can while viewing a photo brings up a "Delete Photo?" button. Even so, that only moves it to the Recently Deleted album. Permanently removing it requires another delete with confirmation.
It may seem that the motivation behind "Are you sure?" is to prevent rash decisions and changes of heart. The official White House photographer isn't allowed to delete any shots, so that solves that problem. But for everyone else the little prompt quickly becomes part of a two-button sequence that finds its way into your muscle memory.
More commonly this second layer of confirmation averts legitimate mistakes. If I'm in a UNIX shell wanting to delete a file and it turns out to be write protected, then I thank whoever decided that a little "C'mon, really?" check was a good idea. Or I might unintentionally delete a video when making a clumsy attempt to grab my falling phone, were it not for those three familiar words, waiting, visible through the cracked screen.
But now there are better options, especially given the prevalence of touchscreens. The ideal is something easy to remember, easy to do, but that's naturally outside the realm of normal input. Here are a few.
Imagine tapping an image thumbnail four times. The first selects it. The subsequent taps expand the image, as if it's being inflated, until the fourth pops it and deletes it.
If that's too much fun, and you find your nephew has popped your entire photo library, touch each quadrant of an image in sequence. It doesn't matter which you start with, as long as you get all four. As you tap, that quadrant disappears, then with the fourth it's gone.
Long-holds are little used on touchscreens, so there's another possibility. Don't display a quit button in a game; hold your finger in the same place for three seconds. After a second, a circle starts shrinking toward your fingertip, to give feedback. Don't want to quit? Lift your finger.
These are only examples, and I know there are other approaches. There are some basic usability issues as well, such as how does an uninitiated person know about the four-quadrant tapping? But it's worth trying different ideas rather than, once again and without thought, following the "Are you sure?" model, the same one that prevented unintended MS-DOS disk formatting in the pre-Macintosh days.
(If you liked this, you might enjoy Virtual Joysticks and Other Comfortably Poor Solutions.)