Nearly 20 years ago, after a chess-playing computer called Deep Blue beat the world grandmaster Garry Kasparov, I wrote an article about why humans would long remain the champions in the game of Go.

“It may be a hundred years before a computer beats humans at Go — maybe even longer,” Dr. Piet Hut, an astrophysicist and Go enthusiast at the Institute for Advanced Study in Princeton, N.J., told me in 1997. “If a reasonably intelligent person learned to play Go, in a few months he could beat all existing computer programs. You don’t have to be a Kasparov.”

That was the prevailing wisdom. Last month, after a Google computer program called AlphaGo defeated the Go master Lee Se-dol, I asked Dr. Hut for his reaction. “I was way off, clearly, with my prediction,” he replied in an email. “It’s really stunning.”

At the time, his pessimism seemed well founded. While Deep Blue had been trained and programmed by IBM with some knowledge about chess, its advantage lay primarily in what computer scientists call brute-force searching. At each step of the game Deep Blue would rapidly look ahead, exploring a maze of hypothetical moves and countermoves and counter-countermoves. Then it would make the choice that its algorithms ranked as the best. No living brain could possibly move so fast.