Although Louis Sullivan an American architect first used the phrase "form follows function" in the late 1890s in an architectural article, the more practical origins of form follows function are to be found in the ideology of the Bauhaus School the influential design school from Germany that emerged during the early part of the 20th Century [1919-1933]. The products designed at the Bauhaus can provide us with excellent examples of success, and often conflict, between the concept of form following function. 

The concept of Form follows Function describes how the form or aesthetics of an object should derive directly from its function. There should be no additional or extraneous elements or flourishes. The thinking is that the function of the object should be explicit (easily recognizable to the user) and accessible (the form of the object should allow the user to readily engage or use the object).

There can be tension or conflict between form and function when developing new products. A piece of clothing should be both comfortable and fashionable. However, these two goals can sometimes conflict. A piece of clothing that is very fashionable may not be very comfortable.

In some cases, the designer may be able to find a way to satisfy both goals without making a compromise. For example, a chair designer may be able to create a chair that is both comfortable and fitting in a minimalist modern interior by using innovative materials or construction techniques. 

In other cases, a designer may have to make a more difficult trade-off. A car designer for example may have to choose between making a car more aerodynamic or making it easier to get in and out of it.

Designers may face choices over what to prioritize in their design. Design teams consist of marketers, engineers, ergonomists, and designers, each with their own perspective of what is important in a design. A marketeer, for example, might prioritize the form of a design over the function because they view aesthetics as an important selling feature of the design. An ergonomist might view the efficient, comfortable, and effective function of the design as of paramount importance. An engineer might advocate for a design that is easy to disassemble for repair or disposal. 

Practical function refers to the ability of a product to fulfil its intended purpose or task effectively. It encompasses the physical attributes and operational aspects that enable a product to perform its designated role. For instance, a stapler's practical function lies in its ability to fasten papers together securely, while a chair's practical function lies in its ability to provide comfortable seating.

Psychological function, on the other hand, delves into the emotional and cognitive impact a product has on its users. It encompasses the intangible aspects of design that evoke feelings, perceptions, and associations. For example, a stapler with a sleek and ergonomic design may enhance productivity and organization, while a chair with a plush and inviting design may promote relaxation and comfort.

While practical function addresses the "what" a product does, psychological function addresses the "how" it does it. Both functions play crucial roles in successful product design, as they influence user satisfaction and behaviour.

Effective product design considers both practical and psychological functions to create products that are not only useful but also emotionally resonant. By understanding the interplay between these two aspects, designers can craft products that foster positive user experiences and build strong brand connections.