A common reaction to my explanation of whether dragging a file will result in a move or copy was that there should be a setting that lets you change the algorithm by which Explorer decides whether you want to move or copy. There are a few reasons why this is a bad idea. First, if there were such a setting, then it removes some of the predictability from the user interface. One of the benefits of a common user interface is that once you learn it, you can apply the rules generally. But if each user could customize how drag/drop works, then the knowledge you developed with drag/drop wouldn’t transfer to other people’s machines. Some people view infinite customizability as a good thing. But each added bit of customizability increases the possibility that a particular combination of settings won’t get tested as heavily as perhaps it should. (“What do you mean, this doesn’t work if you have the notification icons set to hide after only 5 seconds, the taskbar’s auto-hide delay customized to a value larger than 5 seconds, the taskbar buttons customized to a boldface font larger than 14pt, and drag/drop operations defaulting always to move? How could you have missed that combination in your testing? Surely you should have anticipated the interaction between an auto-hide delay longer than the notification auto-hide delay combined with a nondefault drag on a network with fewer than 50 machines!”) Infinite customizability also means that you can’t just sit down in front of somebody’s machine and start using it. You first have to learn how they customized their menus, button clicks, default drag effects, and keyboard macros. “Oh, on this machine, you paste by shift-right-clicking. Sorry. On my machine, I use ctrl-alt-middle-click to paste.” Imagine if everybody could easily customize the order of the clutch, brake, and gas pedals in their car to suit their fancy. There is also the branding element. Like the Mac, Windows tries to cultivate a specific “look” that makes people say, “Hey, this computer is running Windows; I know how to use it!” My DVD player and my car both show the manufacturer’s logo when they are booting up. So too does Windows.

Even if the “change the default drag/drop behavior” option passed “settings court” and was deemed worth the additional test cost, you still have the problem that it affects only Explorer. Other programs would continue to use the old algorithm, at least until you found their settings to change how they perform default drag/drop as well, if such a setting existed at all. Imagine the confusion if Windows Explorer followed one set of rules, but Microsoft Outlook followed a different set of rules. “Oh right, this is a mail message I’m dragging; the default operation is going to be a move, not a copy.”