In The Art and Science of Dealing with Difficult People, author David Brown lists "key personal qualities needed to develop good relationships."
Here are some of the key qualities he identified,
Respecting other people's values, beliefs, and opinions.
Having the courage to accept pressure and face conflict.
Being open to new ideas.
Seeking first to understand, then to be understood.
Accepting that differences are okay.
Building trust and/or credibility before seeking to bring about change.
Judging other people's performances, not their character.
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