The context of the following conversation is Since their mom dropped them off a bit early on her way to work, Robin always started school early.:
Robin says We're always the first ones to get to school..
The friend responds You're usually here before I arrive..
Robin responds My mom leaves early in the morning..
The friend responds Why does she leave so early?.
Robin responds She has to get to work at a certain time. That's why we always arrive early to school..
The friend responds Oh, I see. I wondered why you're always here before me..