There are two main ways of thinking about complex problems: top-down and bottom-up.

• Top down means thinking about the problem as a whole, and how it could be broken up into a few smaller pieces. Then each of those smaller pieces could be broken into even smaller pieces.

• Bottom-up means starting with tiny chunks that are so simple we can already solve them, and using them to build gradually larger pieces, until you’ve solved the problem.

Some people like to start with top-down thinking; others prefer bottom-up. Usually we need to use both.