Psychology in interface design:
20 laws of UX

1. Jakob's Law 1/20
Originally published on Software Development Hub blog by Daria Kyrychenko , Designer.
Jacob' s Law was named after Jacob Nielsen, the researcher and usability expert, head of
Nielsen Norman Group. The law states that users spend most of their time on other sites,
so they would prefer the site that would work in the same way as those ones the users are
already familiar with.
There are already established design patters that can make the design process simpler.
Sticking to existing user-friendly models, we can simplify users“ perception of our site
without forcing them to follow the new conduct. However, if the site is aimed at making a
peculiar impression on the user, it might be worth ignoring limitations. Before designing it is
necessary to start from working out the purpose of your future site in detail.

2. Miller’s Law 2/20
Miller's law testifies to the fact that generally a person is able to store only 7 (+- 2)
elements in their memory. Therefor, to reduce the cognitive overload, it is recommended to
group the content in units of 5-9 elements.

3. Fitts’s Law 3/20
Paul Fitts, a psychologist, who researched human motor system, foud out that the amount
of time required to reach a target depends on the distance and the target' s size. Therefore,
the user's target (buttons, other clickable elements, etc.) should be sufficient enough to be
selected and clicked. Besides, the distance between such objects should also be sufficient,
so that the user could detect and distinguish them.
Read also: 16 UI/UX Design Trends for Medicine Mobile Apps 2023

4. Hick’s Law 4/20
Hick’s law is an experimentally proven theory, saying, that it takes more time and effort to
make a decision if the number of available options is increasing.
That is why, to reduce the cognitive overload on the user, it is recommended to break
complicated tasks into smaller steps, avoiding pouring the whole amount of information or
actions immediately on the screen. Otherwise, it might take him quite a lot of time to
perceive, which might cause them to leave the site or application.
It is difficult for the user to make a choice when s/he obtaines the whole content at once.
This is the reason why Netflix, for example, to encourage the user to make choice quicker,
created a new section named "Top 10 in your country"

5. Law of Proximity 5/20
The law of proximity indicates that objects, that are located close to each other are
perceived as a group of objects. Principles of the law of proximity enable users to perceive
the content easier at a glance. Even if the objects have strong differences, but are close to
each other, visually they will be perceived as a group.

6. Law of Occam’s Razor 6/20
Occam's razor is a rule in science and philosophy, according to which, of several possible,
equally complete explanations for something, the simplest one should be chosen. In design,
this means adding complexity to the design only in case of exceptional need, so it is vital to
analyze the interface and remove anything that might be extra, as long as the removal
does not harm the interface. Getting rid of complexity, the interface will become more clear
and efficient.
A good example is Apple. Steve Jobs' philosophy contained Occam's razor. His iPad and
iPhone prove that: a single button on the front panel of a seamless standalone device.
Google, which directs users' attention to its main function, is another one. Nothing extra.

7. Law of Prägnanz 7/20
The law states that the human eye perceives and processes simple figures more easily
than complex ones. Even a complex and ambiguous object is interpreted by a person as a
simple figure, because it takes less cognitive effort. Simple shapes are easier to read and
easy to remember for the user

8. Von Restorff Effect 8/20
It is also called the effect of isolation, which means that among similar objects, the user
will remember the one that differs from the rest. Therefore, it is recommended to visually
separate important information or an important object.

9. Pareto Principle 9/20
Many people know the law that states that 20% of the effort give 80% of the result, and
the remaining 80% of the effort provide only 20% of the result. Therefore, it is
recommended to focus your efforts on those areas that will bring maximum benefit to the
majority of users of the interface first.
Let“s take navigation in an application, for example. 20% of the functions of the application
are usually located in navigation tabs, which occupy 80% of the user's time spent in this
application. In other words, these very 20% are the most used functions.

10. Peak-End Rule 10/20
The rule says that users rate an experience based on their feelings at its peak at the end,
rather than ot the average. Therefore, it is needed to analyze which points in your product
are the most important and place them at most effective stages for the user to explore,
focusing them on the main thing.
Also keep in mind that, unfortunately, users remember negative experiences better than
positive ones. This is the reason why, for example, Amazon, in order to improve the user
experience after completing a purchase, shows them the list of items purchased, - this
helps the user avoid the feeling of wasting money.

11. Doherty Threshold 11/20
The main principle of the law is to provide feedback to the system in no more than 400 ms.
Provided feedback from the system in no more than 400 ms, productivity increases,
keeping the user's attention on the site or application. What the user should feel is that s/
he is being interacted with. Therefore, to reduce the feeling of waiting, it is recommended to
add indicators, animations, and messages that allow the user to navigate the process.

12. Law of Common Region 12/20
This law belongs to the grouping laws gestalt. It shows that if the elements are in an area
with clearly marked boundaries, then people naturally perceive the objects as a group. In
the design, for visual grouping of elements, you can add a border of the area, or use a
single background for the group.

13. Law of Uniform Connectedness 13/20
This law also belongs to the grouping laws gestalt. It relies on the fact that objects that
are visually connected by color, lines, frames, shapes, etc., are defined by people as
connected objects.

14. Law of Similarity 14/20
People tend to perceive objects that have a similar appearance as related. Similar elements
in the design can be defined as a single group, for example. Therefore, it is recommended to
visually distinguish links or navigation from regular text.

15. Serial Position Effect 15/20
This law testifies to the fact, that people have a tendency to remember the first and last
objects, rather than others, better. Therefore, to improve interaction with the user, you can
consider this principle when building content or navigation. For example, place key actions in
the far left and the far right corners for quicker memorization.

16. Postel’s Law 16/20
It is also known as Reliability Principle. "Be conservative in what you send and liberal in
what you receive." In design, this means that you need to be prepared for the fact that the
user can enter any data on the site or in the application, perform any unpredictable actions.
It is necessary to provide users with high-quality feedback in the form of validation,
prompts, and to guide the user in the right direction.

17. Tesler’s Law 17/20
Tesler's Law, also known as the Law of Conservation of Complexity. It means that each
system has its own level of complexity that cannot be reduced. It is recommended to
design interfaces that are as easy to understand as possible, but not to simplify the
functions or capabilities of the system, as some users might prefer complexity. For
example, you might give the user more detailed search filters, that is, let the user
"complicate" the interface by him/herself.
Larry Tesler, an American computer scientist who worked in the field of human-computer
interaction (He actually introduced the Ctrl+C, Ctrl+V key combination), argued that in most
cases it is necessary to reduce the complexity of the program, and not to force millions of
users to spend extra minute to use the program due to additional complexity. However, his
colleague Bruce Tognazzini argued that people resist reducing complexity in their lives. Thus,
when the app becomes simpler, users start trying to perform more complex tasks.

18. Zeigarnik Effect 18/20
This is a psychological effect that shows that people remember interrupted and unfinished
actions better than others. According to this law, unfinished tasks remain in the user's
memory longer than completed tasks. The design recommends notifying the user that an
action is incomplete, thus increasing the likelihood of its completion. You can also use
indicators or trackers that will show the degree of completion of the task, thereby
attracting attention to bring the action to the end. The examples are: the degree of profile
completion, an incomplete purchase on the site (basket), a loud title that is interrupted to
intrigue the user, etc.

19. Parkinson’s Law 19/20
Parkinson's law states that the most likely task takes the entire time allocated to it. If, for
example, a task can be done in a few hours, but the deadline for it is several days, then the
employee will do this task for several days. Besides, this law can be applied not only to
deadlines, but also to user interaction with the interface. For more efficient work, you can
define a specific time for the user to perform some action. For example, on the website,
after adding products to the cart, the user has a limited time to complete the purchase.

20. Aesthetic-Usability Effect 20/20
The "aesthetics-usability" effect. Everything is very simple here. An aesthetic and clear
design makes a good impression on users and is defined as more useful and convenient.
The law states that people tend to think that attractive products perform better than less
attractive ones. Aesthetic design can hide some minor usability issues.