Do you remember the anxiety of being picked last for the basketball team in phys ed? Or the pressure of doing an oral presentation right after the coolest kid around in English class? Of course you do! Such events threatened your fundamental need to belong, and so they impacted you deeply at the time they happened.
The desire to fit in is a powerful shaper of behavior. In some cases, social pressures serve us well. Just think that 20 or 30 years ago, smoking in public places, drinking and driving and littering were not only commonplace, but widely accepted. Thankfully, things have changed.