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The Law of Laziness

April 25, 2019

Default-aligned image Tom Cruise, Minority Report, 2002

If you’ve seen the Sci-Fi movie “Minority Report”, you’ve probably asked yourself:
"How cool would it be to have awesome gesture interaction systems instead of the boring office work setup. Waving with your hands, pushing buttons, controlling the whole thing."

Well, bad news. It's not gonna happen – because of you and me.

Our brain is lazy, our body is lazy and all for the reason of saving energy to survive.

This laziness is a law. It's omnipresent, predictable and allows for full determination on how any interaction will unfold for maximum usability.


The Law of Laziness states:
Usability = System reaction / interaction effort (energy and/or time)


You're sitting in front of your laptop and want to send mail from Gmail.

Intention: Send Email
How to get there: Open Browser, Open Gmail, Open "New Email Window", Write Email, Send Email

This will take you about 3 minutes. With an email of 250 words, your fingers will move about 10 meters and consume 1kJ of chemical energy. Your eyes will move around 50 meters on the screen, while the eye-muscles responsible for rotation and focus will consume 300Joules of chemical energy. The mental effort required to visualize all steps to be done, having them in your active memory, executing the steps and gradually updating the state of this process and always having the goal in mind. Thinking of the words to write, converting them into mechanical actions by your fingers, proof reading what you've written and making sense of all this and then finally, making a judgement on whether to press the send button before pressing the send button…
…will capture 0.1% of your daily mental energy reserve.
Assuming an average grown males daily consumption of 10,500kJ (avg. 7kJ/min), the mental effort is 10 kJ.

So instead of sitting for 3 minutes doing nothing, you burn 11.3kJ in chemical energy by creating and sending an email through Gmail on your laptop.

Back to Minority Report:
Low-impact aerobic training burns 1900kJ/h or 31.6kJ/min.

Tom Cruise's physical activity is equivalent to "low-impact aerobic training". This would mean the interaction necessary to send an email with his cool future interaction system requires him to burn an additional 90kJ to send an email in 3 minutes, assuming he requires the same time to achieve this result – not including the increased or decreased mental effort due to the interactivity system.

If humans would naturally like to burn energy for no reason, our most favorable working position certainly wouldn't be in a chair for 8 hours everyday with occasional interruptions. Undoubtedly, if it were up to us, the current mainstream office setup of computer + keyboard + mouse would not exist.

If humans would naturally like to burn energy, our keyboard would be a dance. Just for fun, we would have to press every button with our total body weight, multiple times, to trigger the key. And to move the mouse cursor on the screen we would have to do a push-up for every pixel moved – and be happy about the new displays with more pixels.


→ The current workspace setting of computer, table and chair are very efficient in terms of how much physical energy to put in and how much technological output to get. However only the combination of physical and mental effort decide on the fact whether a system is efficient or not.

→ In AR spatial interfaces, it may be possible to find use cases where a slight increased physical effort pays off for a decreased mental effort.

→ For physical space activities that require back-and-forth switching between a computer, the way to get there and come back is included in lack of efficiency and thus hints for a potential improvement.

→ The Law of Laziness serves as a solid cornerstone for product design decision making.

Last Edited on April 25, 2019, 8:00 PM. Published by Daniel Seiler, edited by Camilla Burchill

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