The phrase “steep learning curve” to describe a difficult-to-master skill is mathematical nonsense. If the horizontal axis of the graph represents time, then the vertical axis is probably supposed to represent effort expended. If a task begins by being very difficult and continues being so for a long time, then the curve would begin high above the zero point on the vertical axis and descend very gradually, producing a shallow learning curve, not a steep one.

Most people imagine a steep learning curve as describing a sharply inclined slope beginning at zero; but logically that sort of curve would describe a task that begins by being very easy and which rapidly becomes harder and harder—not what people mean. The confusion is caused by people’s tendency to think of the curve as if it were a hill to be climbed.

An alternative way of understanding this phrase would be to imagine that the vertical axis represents degree of mastery; but in that case a difficult task would begin at zero and rise very slowly over time—again a shallow curve, not a steep one.

The problem is that most people’s interpretation begins with the vertical axis measuring mastery achieved (zero to begin with), but as they move along the horizontal axis in time they unconsciously switch to its opposite: remaining mastery needed (a lot, right away). This makes no sense. The line needs to stand for the same variable along its whole length to make a sensible chart.

There’s little hope of abolishing this ubiquitous bit of pretentious jargon, but you should avoid using it around mathematically sophisticated people.

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