A sort of simplicity/innocence in talk, dispensing with euphemism and flattery and winks-and-nods and insinuations and exaggerations and incantations. Perhaps not being ostentatious about your education with ten-dollar words might fall under this heading too. As well as the skill of speaking simply and to the point rather than rambling.

Complementary virtues

Contrasting vices

Virtues possibly in tension

How to acquire or strengthen it

Notes and links

Mentioned elsewhere

Inspirational quotes