This reminded me of a hunting related story. Came across a big bad 4x4 in the high country of Colorado that was essentially stuck in a very very small patch of mud a few inches deep. They just couldn't get going, and they had another four wheel drive trying to pull it out with no success. We had a PowerWagon, and while we could drag it skidding out of the mud, they still couldn't move on their own power.
Talk about puzzling, there was just no obvious reason why the 4x4 wasn't moving.
Turns out the day before they had been 4 wheeling in heavy snow. Then, overnight the emergency brake had frozen up. The next morning they could only break loose one wheel at a time (open differential). The other wheel remained securely stopped with the e-brake. The truck didn't move until mid-day!
Everybody gets stuck. It's just a matter of where.