Another guess is that using numbers to describe probability is new enough that our brains haven't had time to evolve any way of dealing with the difference between 33% and 34%. The concept of certainty has been around for a lot longer.
There's a negative pregnant in your statement that makes me think you believe in very recent human evolution. Is there reason to think humans have undergone any biological evolution since the development of agriculture?
Today's post, Zut Allais! was originally published on 20 January 2008. A summary (taken from the LW wiki):
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This post is part of the Rerunning the Sequences series, where we'll be going through Eliezer Yudkowsky's old posts in order so that people who are interested can (re-)read and discuss them. The previous post was The Allais Paradox, and you can use the sequence_reruns tag or rss feed to follow the rest of the series.
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