[avaq]

> I envisioned a plot, with a steep curve: x is time, but what’s on y?

This question really got me thinking, because I've always envisioned a plot as well, but the phrase always made sense to me.

I realized that I think of x being "mastery" and y being "knowledge required". On such a plot, you'd see a steep curve if one needs a relatively large amount of knowledge to progress to the next level of mastery.

I've never thought of it differently, and so never realized that the phrase is ambiguous until reading the article. Upon reflection, it makes much more sense plotting time on x and mastery on y when talking about learning.