Care and concentration are needed on every move. Always keep your tactical radar switched on.
Here is a possible position in the Queen’s Gambit Declined, Exchange Variation.
Black is hunting White’s dark-squared Bishop. He has played f6, driving the Bishop on g5 back to f4.
Then he played the Knight from f6 to h5 to eliminate that dark-squared Bishop altogether.
But Nh5 is a bad blunder.
Quite a few people have fallen into this trap. Can you work out why it was a blunder?