I've started running and an unexpected challenge is boredom. The running is challenging as is, but doing it for ~1h30m has been, for me, well, tedious. I guess that's a byproduct of always being within arm's reach of a phone.
That's why I can't do running. I can't get over the fact that it's a painful way to get from A to A. Some optimizing party of me is always screaming WE COULD JUST HAVE STAYED AT A! Now, if they're is a ball to chase and a game to win, I can run until I fall over...
So yeah, running... not for me.