Yesterday, Bill Gates gave a graduation speech—via Twitter.

By Rob Wile
Updated May 16, 2017
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Bill Gates
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This content originally appeared on Money.

And the richest man in the world has helped propel a psychology book to the penultimate spot on the Amazon best-seller list using just 140 characters.

First published in 2012, The Better Angels of Our Nature: Why Violence Has Declined, by Harvard psychologist Steven A. Pinker, argues violence has actually been decreasing in recent centuries, and attempts to explain what may be driving this phenomenon. Mark Zuckerberg previously named it as a “book of the year” pick.

As the Washington Post first noted, as of Tuesday morning, since Gates’ Tweet, the book has climbed 608,850 percent to move to No. 2 on the overall Amazon best-seller book list, just behind perennial graduation-time best-seller, Oh, The Place You’ll Go!, by Dr. Seuss.

Here’s what Gates had to say about “Angels”:

“[Pinker] shows how the world is getting better. Sounds crazy, but it’s true. This is the most peaceful time in human history,” Gates says. “That matters because if you think the world is getting better, you want to spread the progress to more people and places. It doesn’t mean you ignore the serious problems we face. It just means you believe they can be solved. This is the core of my worldview. It sustains me in tough times and is the reason I love my work. I think it can do same for you.”

You can buy Pinker’s book at Amazon. Here’s Gates’ full Tweet-speech: