All things being equal....
I just returned from, what I thought should be, a short ride. Now I am used to pulling in 10 miles/day (3 in 7 out) in hilly terrain 5 days/week, basically my daily commute. And I've done my share of 20-40 mile rides around my hometown, no problem. But today I had my butt kicked by a little 25 mile rural New York ride. There were numerous hills and descents. 650' plus & minus. But it seemed to take forever. I could hardly finish some of the hills.
Now I have a theory: I was alone and this route was very repetitive. So it became boring. Have you delt with this? Because I am convinced that if there were some distraction, I'd have ridden better.