"A bit of fear keeps them in line"

Not everyone will say this out loud, but a good many parents believe it. Children need to be a little afraid of you. Not terrified, but wary. It's what stops them running wild, and a parent whose children aren't at all afraid of them will be walked over.

I'd separate two things that this mixes up. Respect and fear. What follows is my reasoning.

Respect is when a child does what you ask because they've learned that what you ask happens, that you're fair, and that you're on their side. It's built by following through, by consistency, and by being the same person on Tuesday as on Saturday. Fear is when a child does what you ask because they've learned that not doing it makes you frightening. It's built by the shout. They look alike at ten past six. They come apart everywhere else.

Look at what a frightened child does. They comply when you're there and not when you're not, because the fear is of you, not of the consequence. They hide things. A broken ornament goes behind the sofa rather than being brought to you. They lie, because the truth brings the shout. And as they get older, they stop telling you things. The child who's afraid of your reaction at eight is the fifteen-year-old who doesn't tell you where they were. That's the fifteen-year-old you most need to be told by.

Wang and Kenny's finding from chapter 7 sits behind this. Harsh verbal discipline at thirteen went with more depressive symptoms at fourteen, not just more misbehaviour. A child who's routinely shouted at doesn't only learn to keep in line. They learn something about their own worth from the person whose opinion counts most, and it shows up as low mood. I'd keep that in mind whenever "a bit of fear" seems like a small price.

Then there's what fear does to the parent. If your authority rests on being frightening, you have to stay frightening, which means the shout can never be retired and has to get louder as the child grows and fears less. By fourteen you're shouting at someone as big as you who isn't afraid any more, and there's nothing behind the shout at all. A parent whose authority rests on following through has something that still works at fourteen, because a consequence doesn't depend on your size or your volume.

You're right that children need to know that you mean it. Chapter 5 was about how they learn that. It isn't by fearing you. It's by finding that you're reliable, which is a thing a child can respect without ever flinching from.