How about a sequence on math? In fact there's room for lots of math sequences: we don't even have a proper sequence on the math of probability going beyond Bayes' theorem, not to mention statistics, logic, set theory, number theory, information theory, computer science, and programming... All of those and many other subjects are at least as related to rationality as a non-mathematical presentation of quantum mechanics.

If there's interest (e.g., this comment is upvoted), I'll follow up with a poll asking what other sequences people might want. Please suggest other subjects in comment replies, including non-math ones, and I'll include them in the poll.

Eliezer certainly could have written such sequences. Possible reasons he didn't:

• He didn't have time, and it wasn't essential. But now we have many contributors, not just Eliezer. Do we have community interest? I would happily contribute to the extent of my abilities - it sounds like a fun project.
• Other resources already give good presentations on these subjects. They are important to rationality, but they don't need to be presented in a rationality-specific way. Math sequences would not be strongly tied to LW and the other sequences. (This is also true of many other posts outside the Sequences, but that doesn't and shouldn't stop them from being posted here on LW rather than elsewhere.)
• He assumed most or all readers already knew most or all of these subjects. That may be less true of the bigger LW audience today.
• They're good things to know, but they don't contribute strongly to rationality. I would disagree, but that's just my anecdotal personal experience.
• Some of the subjects may have fallen under the umbrella of the Subject That Was Forbidden when LW was young.