Oxford Reference defines mental toughness:
A quality of mind or intellect characterized by, among other things, a refusal to be intimidated, a determination to finish a contest even when things are going badly, and an ability to control emotions and remain highly focused when under the pressure of intense competition.
In a society where our word choices are increasingly directed towards making sure that we do not unintentionally offend, plain-spokenness, tenacity and mental toughness seem to be diminishing. It is unfortunate. In an increasingly complex world, mental toughness, tenacity and being true to self may be more important than ever.