If beef is overcooked, it becomes tough due to thermal coagulation of the protein.
One technique to solve this is the addition of sugar.
Sugar binds protein (mainly collagen) with water, preventing it from tightening.
Using this property, when sautéing thinly sliced beef or pork, sprinkle sugar with salt and pepper to soften it. (Sprinkle 5 to 10 times more sugar than salt.)
Specifically, sugar is rubbed into meat preparations such as ``sukiyaki'' and ``beef stew''.
From here on it's subjective.
When you hear that meat is grilled with sugar, some people may think that it looks unappetizing. However, Japanese people usually eat "sukiyaki" and "beef bowl" with sugar. Also, you may think that if you add 5 to 10 times more sugar than salt, it will be too sweet, but sugar (sweetness) has a less noticeable taste than salt, so there is no problem.