Summarising the idea of microeconomics

I came across the following comment on Scott Sumner’s blog, which really sums up the idea of microeconomics.

You have a straightforward economic argument showing that it is not in people's interest to do X.

You observe lots of people doing X.

There are at least three possible responses.

1. People are irrational

2. X is in the utility function

3. There is a less straightforward economic argument showing that your first argument was wrong.

1 might be true but abandons the economic approach.

2 might be true, but carried out consistently deprives economics of any predictive power, since if you are entirely agnostic about what is in the utility function, any behavior at all might be rational.

3 is more fun, more challenging—and you might learn something.