Design teachers continually ask their students: why? This is frustrating for the student and in the end, ineffective. Daniel Dennet’s two versions of “why?” may help us think this through.
Students interpret this question, I think, as “how come?” In any case, that’s often how they answer it. They start telling us about all the steps in their process, the changes, developments, and other design moves they made that culminated (for the time being) in this particular feature.
The teacher, I think, is interested in “what for?” What is the value or function of this feature? What is the effect? But often, there probably is no intended effect. This is just the first shape that came to mind, or the dimension that fit without causing any explicit problems.
Come to think of it, the student may very well understand that the teacher is asking “why?” in the sense of “what for?”, but when they don’t have an answer, they just start describing their “how come” origins.
And, in fact, it doesn’t really matter whether there is an intended effect to answer the teacher’s “why” question. The answer might be, no reason — yet. Because that’s why “why?” is an interesting and potentially productive question: what might or could the effect of this feature, nut, bolt, angle, or dimension be?
A well considered design is exactly that: rigorously considered. This means that for every ‘independent variable’, for every feature under the designers control, and thus everything the designer is forced to make a choice about, it has been considered what the effect is, what effects could be produced by varying this variable, whether these are positive and could be further strengthened or whether these are negative and could be minimized or compensated for somehow.