As a general rule, you can make lots of assumptions about people from their social media feed. If they’re always changing their profile pic, they’re obviously unstable. If they’re ranting about relationships, they’re high maintenance. Moaning about politics: too self-involved. Reposting old jokes/claiming nicked ones as their own: annoying/untrustworthy. Humble bragging: esteem issues, possibly insane.
As the author notes, all of these assumptions are stereotypes and our judgments of others, based on their posts, may be completely wrong. Yet we have no control over how others view our online posts, through their own “filter” of life experiences. The impact, of course, is that our social media posts may paint a picture of ourselves that is not how we see ourselves. But those posts leave a trail that others use to judge us, and judge us in ways that may be substantially wrong.