I checked the site, and got a 403. Is that what you're talking about? When did you first notice it? The latest Google cache is from Mar 18, 2014 17:37:21 GMT.

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Slate Star Codex

Peripherally associated with the Gwernosphere What Universal Human Experiences Are You Missing Without Realizing It?

Posted on March 17, 2014 by Scott Alexander Remember Galton’s experiments on visual imagination? Some people just don’t have it. And they never figured it out. They assumed no one had it, and when people talked about being able to picture objects in their minds, they were speaking metaphorically.

And the people who did have good visual imaginations didn’t catch them. The people without imaginations mastered this “metaphorical way of talking” so well that they passed for normal. No one figured it out until Galton sat everyone down together and said “Hey, can we be really really clear about exactly how literal we’re being here?” and everyone realized they were describing different experiences.

etc.