The distance between how much a tool feels like it helps and how much it measurably does. It can be large, it can point the wrong way, and the person inside it can't see it from there.
An agent makes work feel easier. Waiting feels like resting, and a wall of new code feels like progress. So "it makes me faster" is no evidence, even when you say it in good faith, and a strong candidate knows that about their own impression.
Say it to your agent
“Don't tell me this was faster. Run gh pr list --state merged --limit 40 --json createdAt,mergedAt,additions,title and give me the median time from open to merge before and after the date I started using you for this work. Then say what that can't prove, since nothing was randomised.”