I am an educator by profession.
In my 35 years of service in the profession I have seen many extraordinary teachers. All left/leave a positive and long-lasting mark on their students. In fact, I'm the beneficiary of numerous teachers/coaches/counselors/principals/superintendents/professors of that ilk.
It's not enough, however, to only leave a mark on our students. While leaving a mark on our students is extremely important, we also have the responsibility of leaving a mark on our profession.
How might we do that? Through mentoring the next generation of professional educators, through pushing the boundaries of our craft in order to broaden its scope and effectiveness, in sharing what we have learned about the teaching-learning process with others, by engaging in substantive discourse about getting better at our work (both as teams and as individuals).
I suspect that that kind of mark leaving applies to all professions. While serving the "customers" is a laudable thing, advancing the profession is equally important.
If the profession matters to us, that is.