“Facial displays are not fixed, semantic read-outs of internal states such as emotions or intentions, but flexible tools for social influence. Facial displays are not about us, but about changing the behavior of those around us.”
This one gets a little technical, but the underlying idea is worth understanding.
Science Direct shares recent research that reveals facial expressions are tools for social influence.
For example, when somebody smiles it’s not because they’re happy — it’s because they want the person they’re smiling at to play or affiliate with them. When they scowl, it’s not because they’re angry — it’s because they want the person they’re scowling at to submit to them.