15 August 2011

Simple, Natural, Intuitive... Back to the basics : Towards a principle of least action for UX Design

Simplicity vs Complexity
For a few years, simplicity has become a hot topic in design of products and interactive systems. Sometimes, it's also the source of some hot discussions in the UX community when the subject of complexity comes back to the front stage, like here, here and here.

When Natural & Intuitive mean obvious...
If your job is creation of interactive systems that meet user needs and if you do a good work, how many times did you hear "... it seems so natural and intuitive", "... of course, it's so obvious" or "why would you do it any other way?" ? Up to you to consider these sentences as congratulations or a judgment about the difficulty of your job... Is it possible that UX Design is only that : a very simple activity aiming to apply a few principles to reach simplicity and obviousness ?

Back to the past : The principle of least action in physics
The principle of least action is one of the main principles of physics. The roots of this principle can be found in Fermat's works about optics, around 1650. For his needs, Fermat uses the following principle "Nature always acts by the shortest and the simplest ways". One hundred years later, Maupertuis improves this principle and extends it to the study of optics and mechanics. With his principle, Maupertuis states that "Nature is thrifty in all its actions". Finally, Lagrange will define some years later, the mathematical form of the Principle of Least Action, which is still used nowadays.

Towards a principle of least action for UX Design
Can we define a similar principle for UX Design ? Until we have a mathematical formula, I propose you to retain this principle:
"All others things being equal, among several alternatives to achieve a goal, a person will choose the alternative that minimizes the effort required or maximizes his comfort."
Here's a very simple example : The Command Line Interfaces (CLI) are known for providing a good productivity but also for requiring a strong effort to learn and memorize command lines. The Graphical User Interfaces (GUI) were quickly adopted because they use existing cognitive skills to reduce the effort required to use the system.

So, is it so simple ?
If you accept this principle, building a good product seems quite simple, since it seems your best bet is the "lazyness" of users. Is it really so simple ? Of course not ! Let's see why in the details of this principle.

"to achieve a goal"
  • You'll be able to build a good product only if you can define and understand in details what is (are) the goal(s) of your user(s).
"among several alternatives to achieve a goal"
  • Several alternatives may exist to achieve a goal. Some of these alternatives may even exist outside of your system.
  • Achieving a goal can be simple or complex (composed of a sequence of several alternatives).
"among several alternatives to achieve a goal, a person will choose"
  • The subject is a person doing a choice. Knowing and understanding the knowledges, motivations and cognitive models of this person are required to build a good product.
  • As UX Designer, Ergonomists or Developers, we only scratch the surface of the problem. As already said by some experts, there's a psychologic dimension, a social dimension and an anthropological dimension to these problems.
  • Moreover, notice that an alternative exists if the person is aware of this alternative and knows it will help him to achieve his goal.
"among several alternatives to achieve a goal, a person will choose the alternative that minimizes the effort required or maximizes his comfort."
  • The choice is an action realized at a particular moment and it allows to minimize (maximize) immediate effort (comfort) required (gained).
  • Moreover, notice that if the principle of least action is a principle which aims to minimize immediate effort, human beings have this particularity that sometimes they can accept an immediate bigger effort, if it allows them to gain more comfort later. Does it mean that our principle is erroneous ? Of course not, but it implies that we must be aware that a person can decide, temporarily, of a different main goal. For example, if a person decides (or is obliged) to learn the usage of a CLI Interface, temporarily his main goal is not the copy of a file (or anything else) but is learning how to reach this objective with CLI interfaces. The effort to achieve this goal is not minimized, but the person will choose, at each step, the alternative which minimizes his effort:
    • the person will choose the alternative which allows her to learn usage of the CLI interface with lower effort (online help, tutorials, books, ...)
    • the person will choose the command line which allows her to minimize effort to achieve the final goal (copy of a file or anything else).
"All others things being equal, ..." (Ceteris Paribus)
  • You can apply this principle if you take into account that you may have omited some others factors...

What can you do with this principle ?
Better understanding of some others concepts
If we come back to the concept of simplicity, we now understand that if simplicity isn't a principle, it can be a powerfull help to decrease cognitive effort. Simplicity is, in many cases, a usefull way to meet users needs. Similarly, if "Natural" and "Intuitive" are not principles, they could be good concepts to help us to decrease cognitive and physical efforts required.

Evaluate if your solution is "bad"
This principle will be usefull to detect if your solution could fail. Indeed, if there's another existing solution allowing to achieve the same goal with less efforts, you should wonder if your solution is a good solution...

Estimate the opportunities for your solution
Even if your solution seems bad, it could be usefull if you try to enlarge the bounds of its applications. Indeed, this solution could be really adequate in some specific contexts or for some specific users. Once again, think to the example of CLI and GUI interfaces. In this case, you'll have to determine ROI of this solution according to its potential market. But this is another story...

To conclude
Next time someone tells you that your solution seems so obvious, just answer "Ceteris Paribus" and smile.

NB: If you know a counterexample to this principle, please feel free to share it !


  1. i agree now,,,
    thanks for solution, thanks u somuch,,,

  2. thanks for informations, and continue succes for you, cayoo