Sometimes a student asks to learn a certain piece and I would say no. Sometimes a student asks to perform a piece for a student concert and I would say no. Why?
It is something like: a runner has completed a 5k and has never done more than 5k. Now s/he wants to run a half marathon. That’s quite a jump from 5k to 21k which is not to say it is impossible. The journey or training to do so would be much more extensive or over a longer period as compared to going from 5k to 10k. I’m sure there are different approaches to it. Some trainers might say absolutely to the runner’s desire to do a half marathon (or even a marathon from a 5k). I imagine there’s going to be significant changes to e.g. the runner’s lifestyle, diet, habits, life goals.
As an educator, I would definitely suggest a 10k to the runner as it’s more attained, the muscles and endurance gained while training for the 10k adds to what s/he will need for the half marathon. Training for the half marathon becomes much easier then. And in this age of instant gratification, completion of another 10k running goal comes relatively quicker when compared to running a half marathon.
That’s why I say no to a student.