Opening Traps
The opening is an important part of the game. You can lose immediately after the opening because you did not follow one of the opening principles. The opening traps are another way to lose.
Opening traps arise in the variations of a line. That is why some people don't play a certain line. They usually win material and put the opponent on the tip of the knife before the middlegame. Because of these criteria, it is important to get familiar with opening traps. I am not saying study every opening, I am saying that you should watch out in the openings in open positions. It is harder in closed positions to penetrate and win a large amount of material, so you will probably still be okay even if you do fall for the trap.
Just like every other type of puzzle, they have to be practiced over and over to become stuck in your brain. So try your hand against these puzzles and then study the big book!