In a chapter from The Handbook of Social Psychology, 4th Edition, Gilbert notes that people have a
an odd habit and a not so odd habit. The not so odd habit is that they describe behavior that is driven by extraordinary dispositions as having been driven by extraordinary dispositions. The odd habit is that they describe behavior that is driven by ordinary dispositions as having been caused by external agencies.
This may sound like a lot of unnecessary jargon, but he immediate breaks it down (Gilbert is an extremely clear and entertaining writer and definitely worth reading):
When one runs screaming from a baby rabbit, one usually owes the bystanders an explanation. Such explanations are acceptable when they are couched in terms of one’s extraordinary dispositions–for example, “I have a morbid fear of fur” or “I sometimes mistake baby rabbits for Hitler.” On the other hand, when one retreats from a hissing rattlesnake, one does not typically explain that behavior in terms of ordinary dispositions (“I dislike being injected with venom” or “I feel death is bad”) but rather, in terms of the stimuli that invoked them (“It shook its thing at me”).
This turns out to be part of a broader phenomenon in language, as Gilbert notes. People tend to avoid saying the obvious and focus on the unusual (Grice was probably the first to notice this). This might seem like a very reasonable thing to do, but there is nothing necessary about it. That is, it’s easy to imagine people who are as likely to state the obvious as the non-obvious (and there in fact seem to be some people like that, at least in sitcoms).
What I think is the most interesting part of this, though, is not that people tend to state the non-obvious, but we as listeners expect the speaker to do this. That suggests either some very sophisticated learning or evolution. (The fact that young children are terrible at distinguishing the obvious from non-obvious in conversation doesn’t mean that it is a learned skill; it could be a genetically-programmed behavior that simply comes online later in development, just like puberty.)