Why do some people prefer Windows XP and Mac OS X over Windows Vista ? After all, Vista is pretty and sleek and much more advanced than XP, and, in many areas, Mac OS X. Why is there so much love for Xbox, but none for Windows Mobile ?

Why do BlackBerry users love their BlackBerrys, but the public is lukewarm about Palm devices?

Why is the Amazon Kindle, which is an unsophisticated, clunky, poorly designed gadget so popular with owners?

Why do people love plain, ugly Gmail?

The answer to these questions is a mystery to most of the companies that make PCs, gadgets, consumer electronics devices and to software makers. The industry spends billions on usability testing and user interface design. Unfortunately, that money is mostly wasted.

The problem is that there are too many technologists in technology. The technology is only half the equation. The other half is the human, that irrational, impulsive, impatient, power-hungry gratification machine.

When you ask someone what they really want, they won't tell you the truth because they're not aware of the truth.

Both users and product designers alike talk about user interface (UI) consistency, usability and simplicity, and system attributes like performance and stability. What's missing is that these attributes are means to an end. The real issue is always the user's physiological feeling of being in control. And control comes in many ways:

Consistency: Designers focus on UI "consistency," but why? Consistency gives predictability, which gives users a feeling that they know what will happen when they do something -- even for the first time. It's a feeling of mastery, of control.

Usability: One of the errors software and hardware designers make is to base their UI decisions on the assumption that the user is an idiot who needs to be protected from himself. Give this moron too much rope and he'll hang himself, the reasoning goes. But instead of taking the Microsoft route -- burying and hiding controls and features, which protects newbies from their own mistakes but frustrates the hell out of experienced users -- it's better to offer a bullet-proof "undo." Give the user control, let them make their own mistakes, then undo the damage if they mess something up.

Simplicity: Simplicity is complex. And there are many ways to achieve it. One way is to insist on top-to-bottom, inside-and-outside simplicity. Extreme examples include the original Palm Pilot organizer, Gmail and RSS feeds. And then there's the illusion of simplicity, which is the Microsoft route. In trying to be the operating system vendor for all people and all tasks, Microsoft Windows and Windows Mobile are extraordinarily complex pieces of software engineering. To "simplify," the company hides features, buries controls and groups features into categories to create the appearance of fewer options, without actually reducing options. (From all accounts, it appears that Windows 7 will offer more of the same.) Both extremes result in something you could call "simplicity." But one version thrills users by putting them in control. The other frustrates them by taking away control.

Performance: Everyone hates slow PCs. It's not the waiting. It's the fact that the PC has wrenched control from the user during the time that the hourglass is displayed. That three seconds of staring at the hourglass is three seconds when you feel utterly powerless. Fast computers are good because they keep the user in control.

Stability: Designers focus on system "stability," but it's not because they worry about time wasted, though that's how users tend to talk a lack of stability. Like the performance issue, instability is about the theft of system control from the user. People waste all kinds of time on all kinds of things, and usually don't mind doing it. What enrages people is when somebody else forces wasted time on you. Blue Screens of Death are more akin to running into unexpected traffic jams or having somebody take away the TV remote control. You're forced into putting your objectives on hold, and left feeling powerless.

One reason for the industry-wide pandemic of frustrating products is that the whole culture of usability testing doesn't emphasize user feelings of control. Microsoft does usability tests, for example, but its tests are flawed. Typically, it sits random people in front of a PC in a usability lab. Victims are directed to do various tasks, and asked what they're doing and thinking as they try to complete those tasks. All of this is monitored, and everything is recorded.Microsoft usability testing tends to focus on enabling users to "accomplish goals." Microsoft categorizes these goals according to their educated preconceptions about what people are trying to do based on their jobs or user categorization are you a student, middle manager, designer, for instance. So Microsoft focuses on results.

My view is that how the user feels during the process is more important than anything else.Here's the problem. In these scenarios, users are using somebody else's PC. They expect and assume that the software is in control. There is no psychological feeling of "ownership" over the equipment or the software or the work or anything. So the most important element -- the sense of control people feel when doing their own work on their own PCs in their own homes -- is missing entirely from the tests.

During usability tests, users are asked constantly about the software. And that's the wrong question. When real people are doing real work, they're focused on their own desires and objectives and are frustrated or not frustrated based on the degree to which they're given what they want.

My advice to Microsoft is to add an additional test: a "Who's In Control?" test. After performing a task, ask the user to rank their experience on a scale with "me in control" on one side, and "software in control" on the other. Try all test methods for completing various tasks, and choose the one ranked with the maximum "me in control" score. And they need the home version for ongoing testing in the "real world."

We've all experienced the full range of emotions while using gadgets, PCs, phones and software. At one end of the spectrum is a kind of thrilling joy, where something "just works." At the other end, there is a consuming rage. The amount of time your emotional state spends at one end of the spectrum rather than the other is the one and only thing that determines how much you "love" the product.

All the factors involved in using a PC -- consistency, usability, simplicity, stability, performance and even the successful completion of tasks -- all come down to control.Give me control, and I will love your product. It's as simple as that.

Mike Elgan writes about technology and global tech culture. He blogs about the technology needs, desires and successes of mobile warriors in his Computerworld blog, The World Is My Office . Contact Mike at mike.elgan@elgan.com , follow him on Twitter or his blog, The Raw Feed .

This story, "Memo to Vendors: Here's How to Build a Winner" was originally published by Computerworld .