This article in Fast Company gives some good examples to illustrate how kindness has the"power to motivate teams, boost productivity and foster a culture that attracts and retains top talent" whereas niceness often evaporates under stress, conflict, and adversity.
According to the author, Kelly D. Parker, research by the "Association of Professional Executives of the Public Service of Canada (APEX) found that teams in a respectful, kind environment express 36% more satisfaction with their jobs and are 44% more committed to their organizations."
The article is worth reading to understand the three reasons Parker outlines to cultivate kindness rather than niceness:
Niceness breeds uncertainty.
Nice people want to be liked.
Niceness slows progress.
From a social justice perspective it's the third that is most interesting because "kind people have the courage to respectfully speak the truth, even if they won’t be considered nice for doing so."
Read the whole article: https://www.fastcompany.com/90703936/3-reasons-to-stop-being-nice-at-work