Politeness Principle
The politeness principle states that students are better prepared to learn, or more motivated to learn, if the advice and feedback they receive from a teacher or tutor is polite and friendly.
The sense of politeness meant here is taken from the work of Brown and Levinson.
Brown, P. and Levinson, S. C. (1987). Politeness: Some Universals in Language Use. Cambridge University Press, New York.