No, nobody knows chess, really.
In the Soviet Union, in the beginning of the '60s, Spassky, an upcoming young master at the time and Kotov, one of the fathers of the Soviet chess school, were having a match when Kotov played an illegal move. (He castled long, but his king was in check).
The room went silent until Spassky finally said:
''Master Kotov… that was an illegal move''.
The move was replayed and Kotov found another move out of chess and despite some difficulties, his position remained superior and he won the game anyway.
But he said that after leaving that tournament, where he, the great Kotov had missed a simple check at the end of his calculation, he said to himself: ''I knew that my best years were now behind me.''.
So you know…
No. Nobody knows chess.