Why? Because he was so enthralled with my brother's campaign that he'd come early to soak up all the details. Who the major nobles were, rumors of distant wars, court intrigue... you name it.
After everyone else showed up and we were crawling through a dungeon, we'd come across a coat-of-arms. My friend would know which noble family it belonged to.
If we came across a shrine, he'd know which goddess it honored. And when we were in town and needed help, he'd know exactly which NPC to see.
So what was it about my brother's campaign that made it come alive for Sean and the rest of our group? The details and sense of history played a role, of course.
But what made it feel like a real world was how everything was interconnected: rivalries between NPC's, who the leaders of each city and baronry were, who created the major magic items, etc.
With Scabard's connections feature, you can turn your players into the type that cares about your world - not just leveling up.
And in between sessions, your players are automatically updated on changes you've made to your campaign (except secrets, of course!)