Why is running outside a lot harder?

I can run indoors and on the treadmill for a long time but if I run outside on the track it’s so hard! Even when the weather is perfect =\. I don’t even last 10 minutes.

Is it because I don’t know how to pace myself? Any tips on running outside better? It’s winter so I can’t run outside when it’s like 19 degrees and snowing all the time.