Social media uses several psychological mechanisms at once:

• Variable rewards — unpredictable likes and posts keep you checking compulsively
• Social validation — likes quantify acceptance, hijacking our deep need to belong
• FOMO — the feed never stops, so disconnecting feels like missing out
• Infinite scroll — removing stopping points erases the cue to put the phone down

These mechanisms compound. Each one is mild on its own, but stacked together they make the app far harder to put down than any single trick would.