A little bit about usability: a good portion of designers do not understand the importance of predictability of a function. This short article is aimed to explain the underestimated role of making things as anticipated.
Predictability is all about knowing in advance or feeling the upcoming event. Often, predictable means boring, but not when it comes to usability. People interact with products or services to achieve some goal. Designer's role is to allow the users to reach the goal smoothly. Meaning, the interface should be structured the way the user gets the desired result quickly and effortlessly. Unless, it is the product that is challenging those parameters, for example, a game.
Predictable is right and on place when the user works with a text editing tool or medical application. As an example, the user clicks on a button he estimates, expects, or knows what should happen next. Awkward, unpredictable behavior takes away the user from his goal. Interface elements, in the case of productivity-driven software, should state clearly the functionality behind them. It is broken user experience or wrong product behavior when something random happens.
Planning the interface designer has to think about the positive and negative effects of the predictability. Using unexpected behavior designer has two simple outcomes: accurate and contradictory. Accurate is when it is planned to be a surprise, which is unexpected. Although in the end, it perceived as positive. Meaning, something magical happened on the way, while the user achieved the wanted result. Opposing is contradictory, and it is when a destructive, sudden action happens. Such behavior perceived as random because it takes the user from the planned goal leading to dissatisfaction.