tl;dr:“The obvious benefit to working quickly is that you’ll finish more stuff per unit time. But there’s more to it than that. If you work quickly, the cost of doing something new will seem lower in your mind. So you’ll be inclined to do more.” James demonstrates various examples.
tl;dr:"At Jane Street we use a pattern / library called “expect tests” that makes test-writing feel like a REPL session, or like exploratory programming in a Jupyter notebook - with feedback cycles so fast and joyful that it feels almost tactile. Having used them for some time now this is the only way I’d ever want to write tests."