One's own experiences also teach humility. When one forces themselves to engage in various activities and circumstances, life teaches us many things. Reading allows us to witness the experiences of others, so that there is a great deal of learning by vicarious means. I don't believe that a single mentor is necessarily the best source for wisdom. Whatever we're taught from external sources, invariably must coincide with our own understandings of life and the human condition. Thus, again, experience is probably the greatest endowment of education.
Yes I agree, that virtue is indeed a potential within us all. I would offer though, there are many levels of humility, if we wanted to be more humble where could we look?
I know of one teaching that many would know by heart. Jesus taught us to turn the other cheek and Jesus showed us what it meant to turn the other cheek to the extent of crucifixion. How many of us would practice that level of humility?
Regards Tony