Almost every recipe and preparation comes with an expert tip. It's always worth looking into it, since here you'll find the chef's tips and tricks, helpful informations about alternative ingredients for the recipe, useful suggestions, or possible matching side dishes or sauces.
In the preparation "Dicing onions" e.g. the tip explains and illustrates why onions sometimes have a bitter taste. The reason is a blunt knife. Onion dices which have been rather pressed than cut get glassy edges. Their juice has been squeezed out!