Postel's Law

Synonyms: robustness principle

Postel's Law (also known as the robustness principle) was formulated by John Postel, an American IT scientist. Now his law is used as the basis for many software development guidelines. The law states: "be conservative in what you do, be liberal in what you accept from others". This law is embodied in HTML, which many experts call the reason for its popularity (or vice versa — opinions differ).

Main Principles

  • Provide a flexible interface for the end-users and try to anticipate the most likely steps
  • Ensure the end-users have a complete understanding of everything related to entering and accessing web resources
  • Conduct in-depth marketing research before creating a user experience
  • Process the feedback and consider the needs of the end-users

How to Use It

In the development of user experience you must provide a unified standard for the interaction of the interface of your software solution with the interfaces of third-party integrated applications and hardware that is used by the end-user to work with your software.

For example, when it comes to elements related to text input, you must make sure that it automatically adjusts to the format you need. So you need algorithms related to handling exceptions. This means that non-compliance with the specifications of your software for a string entered by the end-user doesn’t always have to result in an error.

Here are some examples of post-processing user input:

  • Removing extra spaces (including at the beginning and at the end of a string)
  • Automatic conversion of all alphabetic characters to lowercase
  • Autocomplete some fields in forms
  • Support for synonyms of some commands for integration with voice assistants such as Alexa, Cortana, etc.

This approach is precisely what ensures the liberality that Postel mentioned in his principle. By automatically unifying user actions, the interfaces are more conservative, which means they minimize the entry threshold for new users.

Useful Tool


This tool helps to understand the users’ behavior from the very beginning to the finish of their interaction with UI


Jakob’s Law

Jakob's Law states that users spend most of their time on other sites. That’s why they prefer sites that work the same way as all the other sites. For designers this means that it is always better to choose usual design solutions that are familiar to users.

Who is Jacob

Jakob Nielsen is a usability expert and co-founder of the Nielsen Norman Group — UX research and consulting company. In 2000 he described his observations on users’ behaviour. According to Nielsen, users’ feel confused and frustrated when they face uncommon patterns in design. In these cases they tend to abandon tasks and leave the site.

Tips & Tricks

  1. Use familiar UX patterns
    Users should focus directly on products, services, offers and other content, instead of complex and creative innovations in UX
  2. Keep balance
    Sites overloaded with creativity and non-standard elements confuse users. Try to limit the amount of unfamiliar elements
  3. Help users
    Give them clues when it comes to non-obvious patterns
  4. Meet expectations
    The user should feel complete control over your site. Let users' expectations come true, and they will trust the site and probably come back again
  5. Do not deny users’ experience
    Keep in mind the past user experience, focus on it and use it. It’s better than creating something new just because you want to be different

Hick's Law

Synonyms: paradox of choice

Hick's law states that the time needed to make a decision depends on the amount of choices available to a person. The more choices exist, the more time we need.

This law is named after British and American psychologist William Edmund Hick. He and his colleague Ray Human studied the dependence between the number of stimuli and an individual’s reaction time to them. In 1952 they conducted a test.

That experiment involved 10 lamps that lightened randomly. Participants had to choose the one that lightened. The more lamps were there, the more time people needed to choose the right one.

Hick's law formula

How To Use It

1. Reduce the number of choices

When response time is critical to increase decision time. For example, this is important for control system environments and menus. Remember that the less options you give a user, the more likely he performs an action.

2. Break down complex and long processes into smaller steps

For example, you can divide the user registration process into several screens. It will make the interface more user friendly.

3. Keep a balance between reducing complexity and oversimplifying

Breaking down the choices for a series of lots of small chunks can make the user leave before reaching the goal. There are two rules to make small steps work: show how many steps you have and try to limit them to 5 steps max.

4. Use the highlighting to help users to avoid overloading and to make a choice quicker

You can stand out important options for users among the cluttered interface.

5. Categorize choice to navigate users in a website

If one menu offers direct access to every link, it could quickly overload the user.

How To Break The Law

There are situations when infinite choice works great. For example, infinite scroll in Instagram or Tik Tok. At the same time, in both cases actions are so simple that users actually can repeat them a lot of times. It is different with Netflix, for instance. The reduсtion of options here works much better: people like different lists like Trending Now, Top-10 In Your Country, Best Comedies and so on. Such lists help users to make a hard decision — how to pick one film or TV show among thousands.

Tesler's Law

Synonyms: the law of conservation of complexity

Tesler’s Law, also known as The law of conservation of complexity, states that for any system there is a certain level of complexity that cannot be reduced. According to the law, each application has a certain degree of complexity that either the developer or the user has to deal with.



Larry Tesler is a computer scientist who specializes in human-computer interaction. He has worked for companies such as Xerox PARC, Apple, Amazon, and Yahoo. Larry Tesler described the law in the mid-1980s. He argued that complexity does not disappear, but moves from one area to another. When you simplify the system for the user, you will inevitably transfer this complexity to the developers.

Tips & Tricks

  1. Remove the main burden on users at the stage of development and design of the system.
  2. Don't oversimplify. It is impossible to make a product without a single complexity. But by simplifying the system, you make it more difficult to work on it. If you save 5% of the complexity of the application for the user, but add 50% of the complexity for its development, is it worth it?
  3. Balance the difficulty. Carefully decide how much to transfer complexity from users to developers and vice versa.
  4. Before you simplify the processes, analyze whether such a function is required at all.