Dacher Keltner, a psychology professor at University of California, Berkeley, says studies have shown that people who use Botox to hide lines on their face feel less pleasure in response to subtle things around them and aren't able to read other people's emotions as well.

WSJ: Stress-Busting Smiles

That is, if you don't feel like you belong, you are both less motivated and less likely to hang in there in the face of obstacles.

CNN: The importance of belonging