tl;dr:Jeff uses the principle of Chesterton's Fence to emphasize that understanding the original and current roles of a system component is crucial before making changes. The author illustrates this through their experiences in home renovation and complex computer systems.
tl;dr:“Sometimes you have a lot of data, and one approach to support quick searches is pre-processing it to build an index so a search can involve only looking at a small fraction of the total data. The threshold at which it's worth switching to indexing, though, might be higher than you'd guess.” Jeff illustrates cases where full scans were better engineering choices.
tl;dr:A single cache is a security risk, browsers are responding by partitioning the cache. As a result, developers "won't get performance benefits from using a canonical URL over hosting on their own site."