Replace "knowledge" with "required knowledge". It's not about how efficiently you can learn, but how much do you need to learn in a specific amount of time. If

Replace "knowledge" with "required knowledge". It's not about how efficiently you can learn, but how much do you need to learn in a specific amount of time. If you need to learn a lot in short amount of time (which is a hard thing to do) the curve is steep. You can flatten the curve by increasing the time you have available or by requiring less knowledge.