Actually ... the distraction point is an interesting one. I have often ridden up a steepish hill without noticing it because I was deep in thought about something when I began the ascent.
When I first realised that I was doing that, I thought that I must be climbing more slowly because I was not concentrating on making a big effort. Surprisingly, when I checked my times I found that I wasn't much slower than usual.
For obvious reasons that is unlikely to happen on any brutish climb (say > 20%) because you are not going to get up it unless you really dig deep. I do notice it on 6%-10% though; climbs that are steep enough to require a reasonable effort while not being lung-busters.
Ha ha - it happened again today and some ramps WERE steep but I
still didn't notice them. I was cycling back from Thursden towards Widdop (up in the hills between Hebden Bridge/Colne). This is the profile of the climb ...
The ramp from point *1 is briefly about 25%. *1 -> *2
averages 18%. After *2 the road levels off for about 150 metres and then dips down to point *3 where it kicks right back up again. *3 -> *4 averages 16%. *4 -> *5 gives some relief, but still averages 7%. *5 -> *6 averages 20%. *6 -> *7 is easy and then the road kicks up one last time, averaging 11% from *7 -> *8.
I was looking up the hill at point *1 and was fully aware of how tough it was as I climbed there. As soon as I had respite at *2 I started thinking about some software that I am writing. And then to my surprise, I was suddenly at *8 - I had no recollection of riding the road from *2 -> *8, but I could remember everything I had been thinking about my software!
It was a very odd feeling ...