an invitation...........................

Declaring our uncertainty in our beliefs to others makes us more credible communicators.  We assume that if we don't come off as 100% confident, others will value our opinions less.  The opposite is usually true.  If one person expresses a belief as absolutely true, and someone else expresses a belief by saying, "I believe this is true, and I'm 80% on it,"  who are you more likely to believe?  The fact that the person is expressing their confidence as less than 100% signals that they are trying to get at the truth, that they have considered the quantity and quality of their information with thoughtfulness and self-awareness.  And thoughtful and self-aware people are more believable.
     Expressing our level of confidence also invites people to be our collaborators. ... By saying, "I'm 80%" and thereby communicating we aren't sure, we open the door for others to tell us what they know.  They realize they can contribute without having to confront us  by saying or implying , "You're wrong."  Admitting we are not sure is an invitation for help in refining our beliefs, and that will make our beliefs much more accurate over time as we are more likely to gather relevant information.

-Annie Duke,  Thinking In Bets:  Making Smarter Decisions When You Don't Have All The Facts