So I was reading http://www.itsnotarace.org and the rule about showing no indication that you are racing (to the other commuter). It got me thinking - as one's pain increases, the perception of others' pain relative to one's own pain decreases, in turn causing perception of self pain to increase further. Therefore, it seems showing less pain than other riders has a psychological advantage while racing.
Example: During a recent ride, I was thinking "I'm hurting and that dude is totally fine!" I knew it wasn't true (and then at the end he said he just set a bunch of PRs), but it's really mentally challenging when you really don't know how hard he is working.