Curves

My mind's on curves. Not female curves, but something more nerdy. 

• On the one hand, there's the curves of economics.  I'll probably get the terms wrong, but there's a supply/demand curve that shows for any price there's a market clearing point at which supply and demand are in equilibrium.  And implicit in that, or maybe something else, is a curve that shows the marginal cost of producing something declines as production goes up--mass production saves money in other words.
• There's also the learning curve.  The more time you've spent making stuff/learning a subject, the easier it is. 
• Finally in my thoughts is the Pareto 80/20 rule.  Now it's not usually talked of as a curve, but if you visualize it you can see it.  To me, it's the exact opposite of the supply/demand curve and the learning curve.  I used to use it in discussing software development.  It would be easy to do software to handle simple cases, but as the cases got more difficult it would become harder and take longer.

It seems this week I've got more questions than answers; because in this case I can't figure out how the curves work together, if they do.  Or is it just a case of different tools for different situations.