(I translated this article written by Lee Sedol himself, which originally appeared on March 23 on DongA.com news http://news.donga.com/Issue/List/08000000000070/3/08000000000070/20160323/77152796/1 I tried to avoid liberal translation, so the translated sentences may be a bit rough. I will translate more Korean articles when I have time.)

[Lee Sedol’s Review on the Week with AlphaGo] Advantageous Beginning… Winning Flow Lost by Impulsive Greed

<5·End> Regrettable Defeat

(Figure 1 and Figure 2 in order)

The victory in the fourth match made me confident about the fifth match. My confidence was that top pro players could defeat AlphaGo in its current state. Originally, since the fifth match is the last one, stone colors should be [randomly] chosen again, but I chose to play with black. It is the established theory that the Chinese rule is slightly more disadvantageous to black with white’s Deom (Komi) of 7.5 points, but I wanted to prove that AlphaGo could be defeated with black.

For the fifth match, I entered the room with my daughter. I could not do so for the third and fourth matches because of heavy pressure, but this time I did not feel much pressure.

The beginning was as I expected. Clearly, AlphaGo avoids moves like black 17th, and she responded by playing elsewhere (tenuki) as expected. Thanks to that move, I got 40 points in the bottom right in the beginning. I thought my advantage was certain, because one of AlphaGo’s moves in the bottom right was a bad one.

However, a small seed of greed was born in my mind when the focus was to reduce white’s influence in the right and top sides. Figure 1 black 1 (the 69th) was [evidence of] that. It would be advantageous if AlphaGo responds at ’가’ . Since AlphaGo likes to play safely, I thought this move might work. However, AlphaGo adventurously played white 2. This part demonstrates that AlphaGo is at the level of top pros, playing an adventurous move in a disadvantageous situation. Since I already expected white 2, I probably would have played black 1, 2 in Figure 2 in a match with a human pro. In that case, black’s advantage could have continued. It is necessary to respond understanding AlphaGo’s habits, but it is not right to be ambitious guessing her habits.

The fifth match, which ended up as my defeat, was the most regrettable one in this series. I was filled with shame for letting a winnable opponent get away because of a single moment of greed.

The week with AlphaGo felt like a ‘bamboo clapper’ [1]. The weaknesses of ‘Lee Sedol’s Baduk’ were revealed without camouflage. The old rigid ideas of the pro baduk community were shattered. We need to read and review the moves that we have perceived as given.

The result was one win and four losses, but I think now my win probability is 50%. If the time limit is three hours, my win probability may be higher. If Park Jung-hwan 9 dan or Ke Jie 9 dan were to play a five-match game against AlphaGo within a month, they could probably win. AlphaGo is not perfect yet.

Anyway, this five-match game with AlphaGo will strengthen me and the baduk community. I feel obliged to repay people who praised a defeated general [2] like me. I was defeated in the match with AI, but I still believe that baduk has something that cannot be appreciated just by an outcome.

[1] A bamboo clapper (Jukbi in Korean) is a wooden stick used during Seon (zen) meditation. According to the Jogye Order of Korean Buddhism, “The shorter Jukbi is used to announce the beginning and end of Seon meditation sessions while the longer one is used to prevent sleepiness during Seon meditation.” Lee Sedol used the expression to mean the latter one, because the matches felt like an awakening shock to him. http://www.koreanbuddhism.net/bbs/board.php?bo_table=1020&wr_id=11&sst=wr_datetime&sod=desc&sop=and&page=2

[2] In East Asian culture, defeats are humiliating for a general. Explaining the cultural background would be a long story. In the context of this article, Lee Sedol implies that he does not deserve the praise (which was huge in Korea).