Yes, you can become a chess master, here's how: part 4

I left off part 3 with a postion which did not occur in the game. There is a puzzle if you would like to solve it before you read on. 

http://www.chess.com/blog/aww-rats/yes-you-can-become-a-chess-master-heres-how-part-3

Here is the position, which did not occur. The lesson to learn is to know the tactic and use it to your advantage in a future game.

Had Black been aware of the drawing line, he might have steered for the diagrammed position. However, he missed the chance when it actually came up in the game. The next several moves feature some incomprehensioable blunders by both sides.

Let us continue the game. White piles up on the pinned Knight on e7, overlooking Black has counterattacked the White Queen, and she is captured for free. Black castles on move 21, missing the draw. White hangs a Rook on c5, but Black doesn't take it, and for two straight moves. Finally, White does drop the Rook, but the Black King is exposed.

So, now...White has a forced checkmate, but doesn't find it. (Can you?) As a matter of fact, White can also fork the Black King and Queen with her Bishop, a move many of you would make out of simplicity. Instead, White displays a thinking deficiency here and played 29. c3.

Here is your question which I'll address next time. Aside from every other possible move White could have done, why do you think 29. c3 was selected? Can you see the thinking deficiency at play? This game will continue to swing back and forth as the mistakes continue....