1) The lives people showcase on social media are nothing but the highlights of those posting. Very few people post pictures of Excel spreadsheets day after day or gray skies every morning. Rather, they are always traveling, eating, hugging, kissing, laughing, smiling, etc. Those on the viewing end are constantly comparing these highlights to a behind-the-scenes perspective on their own lives. "Keepin' up with the Joneses" has taken on a whole new meaning for today's youth. The are exposed to nothing but glorified versions of friends' (and celebrities') lives which make them feel inadequate, bored, self-conscious, and deprecated.
2) There has been a massive degradation of communication skills among today's youth. No longer to people reach out directly to friends and family to let them know what they're doing, where they are, how their lives are, etc. Rather, they just post this information on some social media platform(s) and assume that anyone who cares will see. Those who spend minimal or no time checking social media are often left in the dark and out of the loop. The art of a phone call has greatly devolved.
3) There is an empirically-verified addictive quality of social media that leads to decreased productivity and indulging of narcissistic tendencies, among other things.