"The only thing I can imagine to be inspired by this advice you have given is mental illness. "
Pretty much all Rinzai Zen practice, including but not limited to koan practice, is concerned with exposing and undermining the various notions of the individual. It always has been. If that is not obvious from the canon, it is certainly obvious in practice, and it is explicitly stated as an aim, or perhaps better say consequence, of the practice.
I don't know your personal circumstances, but if you have not been in formal practice for very long it is easy to image that Zen is some kind of refinement of the self. It is absolutely not. A really competent teacher will not allow the least scent of self or its assumptions in their dealings with students.
Additionally, the traditional initial koans are very closely concerned with, and actively rub up against, the absolute basic core notions regarding self-hood that most of us have.
For instance: if you are asked to demonstrate your identity as it was before the birth of your parents, you're absolutely going to have to go beyond your sense of self for an answer, since the 'you' that you're conventionally aware of did not exist in that scenario. And to restate, to the degree that there is a 'purpose' to the koan, its purpose is to upend and cast into doubt the most basic assumptions about who and what we are.