I can convince you that this pattern of lit-up phosphors looks grabbable by knowing what artists have long known about shadow and lighting to give such elements

I can convince you that this pattern of lit-up phosphors looks grabbable by knowing what artists have long known about shadow and lighting to give such elements affordance (http://en.wikipedia.org/wiki/Affordance)—an http://en.wikipedia.org/wiki/Affordance)—an appearance of tactile actionability. Cognition and perception are remarkably similar across cultures because vision and physiology are remarkably similar across cultures. There's some trickiness regarding cultural implications (for example, colors carrying different connotations across cultures). Navigating and using this shared language to meet your design goals is far more likely to succeed when you're aware of the considerations and use (or break) them consciously. This doesn't mean that all design should trend towards skueomorphism—conventions enter into this process, but convention isn't a nebulous affair either. If your audience isn't particularly specialized, you can rely on them being familiar with the UI conventions of their operating system, to a greater or lesser degree. This means that people will likley try to resize boxes from the lower right if you draw something that looks "grippy" there, unless they're at home in a RTL locale, in which case they might reach for the lower-left first. If you're overlaying resize controls onto a box, how are you going to draw those controls? Will you draw them outside your content—does your environment even allow you to do that? If you're drawing them on top, how do you ensure that they are easy-to-target without obscuring too much of the content? How do you deal with people who have poor sight or other vision defects like colorblindness? What about audiences who might have trouble using a mouse, like the elderly? What if your application has to serve all of these audiences at once? How would you even go about testing the decisions you make? Of course there's subjectivity in how to execute this, but I've just led you through a thicket of constraints that affect your ability to communicate affordance using nothing but the illusion of pixels on a screen. Knowing what parts are science, what parts are convention, and how to effectively meet your design goals requires an understanding of the discipline. _Objectively_, without science your pretty interface might be pretty, but it might be a shitty interface, and you won't know the difference?