Chairs mean you're a stationary adult. Stools mean you're still on the cutting edge.
Chairs mean formality. Or comfort. Or society. Or rules, MAAAAN. But bar stools? Counter stools? They say that we're not gonna get too comfortable. We're nomads. Rebels. We're gonna stand up and move on at any second! Stools are hip, daddy-o. Stools are cool. Yeah. Stools.