The good news is that some masters and grandmasters have published their
repertoires in Bookup ebook format.
That means you can train yourself in a master's repertoire - fast.
That does NOT mean memorizing the master's games.
It means you'll understand what to play against lines that are never seen
in master play, the variations you encounter every day on the internet and
over the board.
Remember how I said masters love to play weaker players who mimic the opening
moves of great players? The games of great players are often tremendous
theoretical struggles where one slight error can cost the game. A master knows
that the weaker player didn't take the time to understand those potential
errors.
So the master gladly plays the opening until the weaker player is in over his
head. Then wham! He takes the weaker player out, often by playing an inferior
move!
But most weak players never study the inferior moves.
Often the weaker player has no plan at all for continuing beyond the opening,
and hopes each game that the opponent will gladly lose with the same moves from
the grandmaster games. How often does that happen? Almost never.
So if the bad news is that you have to study more than just the actual
opening moves of the grandmasters then what's the good news?
Continue