The context of this thread is AlphaGo. Why would we bother discussing what bad human players do when the topic is clearly about play at the highest levels?
The highest level players play special variations against each other hoping that the other player doesn't know it. They CLEARLY play against what they think the other player knows, not what they know (since they have studied this variation on purpose to prepare)
Interesting. From chess it seems that, for important matches, players will deeply study each other's games and try to get the other player into positions that they may be less used to playing and less comfortable with.
Its more important to smoothen out your own weaknesses than looking for your opponents. A weakness in your style of play is going to make you lose way more many games than your ability to find some weaknesses in some other player.
To become a pro you have to go through insane levels of competitions, you need to be strong, not find a weakness in the 100's of players you will face to just have a shot to become the lowest level of professional.
That's just appeal to authority. Lee Sedol's move against AlphaGo in game 4 could be considered a trap because it actually didn't work, but it was complicated enough to trick AlphaGo.
But it's not even a good authority, since strong amateurs (semi-pros) have many opponents (amateur tournaments are played in the same day or weekend and have many matches), while top players prepare specifically for one opponent in tournament finals (each match played on a different day).
As a pro you study everyones games as a mean to get all the latest information possible, but there isn't really much you can do as a top pro to play against your opponents likings: the era were that could bear fruits ended decades ago.
For example, US Congress has a lot of matches in a day so you don't even know who you're going to face. Only top players study the games of their opponents because they have time to prepare in finals of big tournaments.
