Just realized the bus tracker app is actually right most of the time

For about 8 months I refused to trust the transit app on my phone because the first time I used it the bus came 15 minutes early and I missed it. I kept showing up at my stop on the printed schedule like a stubborn idiot, standing in the cold on Rt. 9 in Springfield. Then a guy at the shelter showed me he was watching the little bus icon move on his screen in real time, and sure enough the 7:42 rolled up right when the app said it would. I started checking it before I leave the house and it has been within 2 or 3 minutes almost every morning since January. The early arrival thing still bugs me, though, and I want to know if anyone has figured out why that happens on some routes but not others.