• Main ideas: Present two simple ideas - design decisions have consequences and modules can hide them. Illustrate with design space tree, configuration options, and examples of mistakes. Emphasize focusing on high-level decisions first and using modularization to handle change.
• Key information: Design space is like a tree with leaf and trunk decisions. Configuration options create multiple products. Focusing on leaf details early leads to mistakes. Changing requirements result in abandoned paths. Some high-level decisions are hard to change. Reframe as program families and use modularization.
• Important details: Examples of leaf and trunk decisions like input encoding, memory use. Mistakes like making incompatible leaf-level choices. Difficulty in determining which decisions to hide in modules. Importance of getting high-level decisions right.