"The art of economics consists in looking not merely at the immediate but at the longer effects of any act or policy; it consists in tracing the consequences of that policy not merely for one group but for all groups."
In the same way that "eat food" is a lesson on wilderness survival. Or the way that Schrodingers equation tells you all you need to know about Quantum mechanics.
The rest is just commentary and examples.
The lesson is a clever device by the author, he pwns marketing 101, but is "to grok economics consider future global effects" really that inciteful?
It sure seems simplistic, but again and again we suffer from policies against that simple rule. It's amazing (and depressing) how many problems can be explained by it, like politicians implementing myopic short-term reforms in order to win the next election (and the future be damned), or to appease some selected and influential group (and be the rest ones left to pay it)
"The art of economics consists in looking not merely at the immediate but at the longer effects of any act or policy; it consists in tracing the consequences of that policy not merely for one group but for all groups."
The rest is commentary and application examples.