I enjoy reading books, watching movies, and listening to cds very differently from talking, dancing, or playing music. When I can participate, or even when I'm paying attention with the option to participate, I perceive the activity differently. One reason reading old blog posts or reddit comments is strange is that I'm encountering something that I usually see as participatory but in this case is frozen, the people whose words I'm reading appear to be eager to continue the discussion but in fact have moved on, lost interest, and may no longer share the beliefs they were so excited about.

When I approach something as frozen and fixed, I am much less excited about it. The possibility of asking a question in a lecture, even if I never ask anything, forces me to actually understand the evidence and arguments in a way that I'll lazily avoid when watching a recorded one. When I'm reading a book I either fall into an "accept everything" mode or I need to be constantly thinking about how I would argue with the author [1]. (This can annoy other people in the room who might prefer to do whatever they were doing without the constant interruptions.)

[1] I'm currently reading, influence by robert cialdini, which I encountered positive references to on less wrong. One statement that particularly bugged me was:

just after placing a bet, [gamblers] are much more confident of their horse's chances of winning than they are immediately before laying down the bet. (p57; chapter 3's first sentence)

I believe that gamblers might talk as if they are more confident then, but if they really were more confident, wouldn't they keep buying tickets? If the bookie's odds are 5-1 and I originally put the horses chances of winning at 25%, I might place a $10 bet. But if the placing of that bet caused me to up my estimate of its chances to 40%, might I think it would make sense to bet another $10? My guess is that if you set up an experiment where you asked gamblers if they wanted to make additional bets, they mostly would not, even though they would report increased confidence. So it's not real confidence.