The #1 professional-development spend of 540 engineers isn't a book

I spent a weekend reading all 540 comments from Hacker News' biggest Ask HN on professional development: "What is the best money you have spent on professional development?" (524 points, 540 comments).

The results surprised me — and they might change where you put your next learning budget.

Update (Sep 7): this leaderboard no longer covers one thread. The engine now mines qualifying Ask HN threads on its own and publishes them daily — the site is up to 5 leaderboards, 66 resources, 1,551 comments, zero hand-mining. Details on how that works (and why it refuses to publish junk) in the follow-up article.

The ranking (by how many DISTINCT commenters named it)

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