- People will catch edge cases before they occur

- People will realize that they have an edge case, and write a failing test/trigger the failure before they fix it, and explain it to me

- They come up with an approach pretty much instantly, and their design is correct after thinking about it a bit more

- Their coding style is very functional & composable (idk why I find this correlates with success, but it does)

- They test all dimensions of variability in their inputs

- They focus on what matters

- Forward progress doesn't stop

Things that don't correlate with instinct

- Speed of implementation (within reason). Different people can type at different speeds, and people think at different speeds

- Having to google APIs