The problem is that when we play chess the main tool we use is our short term memory.
In this memory is room for only 6 to 12 items which stay there for about 30-45 seconds.
So ofcourse it is impossible to have a good thoughtproces. Not only all the moves and the subvariations do we try to store in that little space but also the bookkeeping of how much wood we win and loose during exchanges. No wonder that we play so badly!
The trick is that we make use of our long term memory. When the pattern is edged in your brain (i.c. the long term memory) that a bishop or pawn on f6 causes backrank problems for the black king and that mate will follow within 5 moves when a white rook arives on the backrank than can you abbreviate this whole line to one item. So the short term memory has to work only with this one abbreviated item.
The more long lines are stored in your long term memory, the more complex problems you can handle in your short term memory.
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