Aesthetic Usability Effect - Users often perceive aesthetically pleasing design as design that’s more usable.
Hick's Law - The time it takes to make a decision increases with the number and complexity of choices.
Jakob's Law - Users spend most of their time on other sites. This means that users prefer your site to work the same way as all the other sites they already know.
Peak-End Rule - People judge an experience largely based on how they felt at its peak and at its end, rather than the total sum or average of every moment of the experience.
Postel's Law - Be liberal in what you accept, and conservative in what you send.
Zeigarnik Effect - People remember uncompleted or interrupted tasks better than completed tasks.