When I'm on Zwift, I find myself trying to beat PRs, or chasing down that guy(or gal) in front of me, or trying to hold a certain wattage for certain period of time, or do a climb just to see how fast I can go down the other side. It's easy to get a good session in. I've gone as long as 2 hours, and I almost always end up going harder than I planned, whereas without it I can barely go 40 minutes without getting bored out of my skull.
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"Don't take life so serious-it ain't nohow permanent."
"Everybody's gotta be somewhere." - Eccles