It can happen.

I was boarding a transcon after a TATL, I was exhausted, and I was assigned a middle seat in coach for the next 5 hours.

But when I reached my row, the gentleman in the aisle seat asked me if I would prefer to sit on the aisle rather than in middle! I was astounded - he was tall so the middle would be uncomfortable for him, and he didn't seem to be related to the woman sitting in the window seat.

I gratefully accepted, and even offered to buy him a drink when the opportunity arose, but he declined.