SIMPLIFIED TUTORIAL, 1 (in the series where we break down concepts intuitively):
Before we talk about correlation, let's discuss standard deviation, its analog in dimension 1. People don't get while using it as a metric for deviation!
This is simplified of course (n, not n1); sorry nitpickers..
More technical: my book at https://researchers.one/articles/20.0...
Also we wrote a paper (Goldstein & Taleb, 2007) showing PhD students in statmathfinance and fund managers got the point wrong (mismatch between intuition and computation). Yet it is elementary.