(A brief aside on what I mean by inherent complexity: solving some partial differential equation or writing 'I must turn in my homework' one hundred times might both take the same amount of time, but the latter is less complex. Similarly, Dijkstra's algorithm to compute shortest paths might be easier to implement than a form to add a new employee to the database, but it is nevertheless more complex.)
When writing a program, one usually has to juggle lots of balls that move in simple ways. You can make a career out of writing programs that convert data between various mostly equivalent representations (table in database, packet on the network, Python object in RAM, pixels on the screen). I do not want to claim that this is easy: the details of what data ends up where, of how to deal with the not-quite-equivalent representations, of who is able to see what, etc., matter. But solving complex problems of which code to write does not mean that the code solves complex problems.
So it makes sense to use longer names. You have only little attention to spare on individual pieces and s.add(b) is more difficult to understand than submit_form.add(submit_button). Here, adding things to some container is a well-understood concept, you simply want to know which container and which things.
Conversely, when your problems have a high inherent complexity then you end up with a small number of balls that behave in a complicated manner. (If you have many complicated balls, the problem is too difficult to solve.) So you split up your explanation: first you describe the balls, then you assume that the reader knows what they are and give a succinct explanation of their interactions. (Flipping the order sometimes makes sense too.) It is clear that ax²+bx+c = (ax+b)x+c is easier to understand than equals(add(add(mul(parameter_quadratic, mul(variable, variable)), mul(parameter_linear, variable)), parameter_constant), add(mul(add(mul(parameter_quadratic, variable), parameter_linear), variable), parameter_constant)). The latter is simply too noisy, it does not allocate the symbols in an efficient manner to convey its meaning.
However, writing ax²+bx+c assumes that the reader is familiar with the meanings of a,b,c,x and with addition, multiplication and exponentiation. You probably are (else this would have made a poor example), but even if you were not, it would still make sense to explain these concepts first, to enable the succinct explanation.