The Mishnah Avot (2:5) teaches, "A bor cannot be sin-fearing". A bor is an ignoramus, a metaphor borrowed from agriculture. Literally, bor means an unfarmed field, which is left to lie fallow. During the years of famine, the Egyptians begged Joseph for seed (Genesi 47:19) "that the land may not become a waste."
Onkelos translates "waste" into Aramaic as tvor. Leviticus Rabbah discusses leaving fields bayra during the Sabbatical year.
A bor, then, is someone who has left his or her brain to lie in waste, uncultivated. He or she has not applied the tools of culture to his or her raw materials.
The Mishnah in Avot continues, "A bor cannot be sin-fearing… And a timid person cannot learn, nor can an authoritarian person teach." Rashi explains a bor as someone empty of all matters - religious and secular, like a field where nothing grows.
According to this teaching, ethical behaviour or fear of sin is a product of education, knowledge of the world. The responsibility to tend to the field of the mind is both with the student, who must put aside all issues of pride and with the teacher, who must never be impatient.