Everyone likes a smile, right? Well, it's not that simple. Continuous smiling and/or smiling out of context should ALWAYS send up red flags. This is true whether the smile is sincere (which is very often not the case) or insincere.
During her Senate confirmation hearing on Tuesday, Betsy DeVos, the nominee for US Secretary of Education, was projecting a near-constant smile - although, it was rarely a sincere one.
If your aim was to influence a person or group, a near constant or out of context smile will raise suspicions in those who would (otherwise) support your view. The vast majority of those who are "on the fence" or who oppose your ideas or proposed actions will become polarized strongly in the opposite direction.
Witnessing a person who is smiling out of context or smiling constantly feels odd. Instinctively, it makes people feel uneasy. Indeed, if you were an actor - behaving in such a manner would be a good way to project this uneasiness. And if you were an attorney, you would never want your client to behave in such a manner in the courtroom or during a deposition.
Such a constant smile or smiling at the wrong times are some of the primary reasons why most people do not like clowns - for their smiles are painted on.
When we see others smiling this way, it engenders a feeling of emotional dissonance (e.g., Why is this person smiling when discussing a sad subject?).
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