Have you ever wondered why, from time to time, it seems some kind of design waves start from a website and spread all around? This was the case, for instance, with flat design. After a long period of software design, trying to reproduce our real 3D environment, everything on the web started to appear flat, without shades and potentially pastel colored.

Why did that happen? Why did such so many different brains change their minds so suddenly? Was 3D some kind of fashion which changed at a given time, as all fashions do? There was, for sure, some kind of fashion effect on the spreading of flat design; nevertheless, the consistency principle applied here as well. After starting to see the flat design on some of your products, and particularly your most beloved ones, you started expecting this design on all your other products. Moreover, you, me, and all other users like us started feeling uncomfortable with websites and products with different kinds of design. It is like the feeling you get when having to drive an old car after a long time; yeah, I can make it drive me where I want, but why does it have to be that difficult? In that context you have to, in some way, re-learn a bit about how to drive, since everything you are familiar with is there in the car but in a slightly different position or appearance. This increases your learning costs and diminishes your perceived effectiveness.

This is exactly the same effect that justifies the spreading of flat design: once you got used to it, you started feeling as expensive to adapt to different kinds of designs, and since the majority of the users starte experiencing the same feeling, this pushed all the remaining products to adopt flat design as well. Whether or not this was an overall improvement should be evaluated by resorting to the previously introduced principles of clarity and efficiency.

How do we apply this principle to data mining user interfaces? We can do this reasoning about some bigger and smaller features data mining software users are currently used to. For instance, as two small examples; syntax highlights and auto-completion.