[sanderjd]

This is a closer analogy. It has the same "sounds right" appeal, while sharing the problem with confounding variables. But Yglesias' analogy does a much better job of illustrating the problem; it is purposefully absurd in a way that quickly leads to the desired explanation.

I'm finding it interesting to consider all three scenarios together. What is the similarly between your analogy and the book study that makes them sound right while the pants analogy sounds wrong? I contend that it is the aspect of growth through practice. My intuition is that these three scenarios exist on a spectrum with regards to how much affect practice has. It is clear that working out a lot results in more muscles, and it's clear that trying on tall pants a lot does not result in becoming tall. To me, it's also clear that reading a lot of books "exercises" some sort of book-reading "muscle". But it's less clear what the follow-on effects of exercising that muscle might be. It's also not clear whether growing up with either gym equipment or books around usually results in heavy use of those things!

[pram]

At a very basic level, it gives you experience. “Mileage” is important in mastery of subjects.