BEFORE THE TOURNAMENT.
The comparative study of measured relative strengths and weaknesses. Where you are stronger or weaker vis-a-vis those of your opponent etc.
The characteristics of your opponent.
Then you choose your weapon of choice, the opening/variation that will give you your best percentage chance for a win or a draw.
All these happen before you even reach the table. Our GM has estimated this to be nearly 60% of the battle.
AT THE TABLE.
At the table "chess" is played between moves. Between moves, the questions will arise in your mind....have I done my training? Was it thorough enough? Am I making the right decision? Etc.etc.etc.
Doubts or confidence. And if your mind goes negative, you will miss the clues and not be able to seize your chances. Mental chatter. Self doubt. Noise.
Then you make your move. Fear infected decisions or clarity. After the move it starts again. Move after move.
At the end of all this, you win, lose or draw depending on how you have answered those questions in between the moves. Or if you even have an answer.
It is best if many of those questions are answered before the battle. For if they are not, they will certainly be asked during the battle. Ergo, loss of concentration and focus.
That is why it is said that confidence is key.
Interesting isn't it.