A parent who consistently loses their cool and yells and contorts their face and furrows their brow and pops their eyes out and gets red in the face over relatively insignificant things (like when the children got into a fight while parent was trying to concentrate on something important, or like when child fails to complete a task that the parent requested them to do twelve times, etc etc etc.), then the parent loses arguably the most important discipline tool they had: Expressing sincere frustration with the child's behavior. Yes this can and should be a very effective tool. All kids want to make their parents happy and proud. But if the parents lose their cool every other second, it becomes ineffective and meaningless (except that it still harms the child in many cases). So those parents may find that they must resort to hitting for situations like running in the street. Because the normal, healthy way to teach the child that a certain behavior is not ok, has been rendered ineffective due to gross abuse and misuse.