Why do some people always dare not express their true self with duplicity?

Sometimes I really dare not express my true thoughts in my life or work, because sometimes what I say will hurt people, and sometimes I don't know how to express my views, so I can only say something that others can accept more easily, which will also avoid some contradictions. I really don't want to say anything in my work and life, otherwise it will cause unnecessary troubles and contradictions. We still have to learn to keep a low profile and keep our mouths shut.