Why do foreigners always say knock, knock, is there any meaning and allusion?

KK: []

DJ: []

intransitive verb

1. Collision

His leg hit the chair.

His leg hit the chair.

Step 2 knock, knock, hit

He knocked at the door and came in.

He knocked on the door and went in.

3. Knocking sound (due to engine failure and other reasons. )

transitive verb

1. Knock, knock, knock.

The falling bottle hit him on the head.

The falling bottle hit him on the head.

2. Hit (bump) ... [O][O8]

The blow knocked her unconscious.

The blow knocked her unconscious.

Criticism and belittle

The critics criticized her latest novel.

The critics belittled her latest novel.

Noun (short for noun) [C]

1. Knock on the door; Fight, fight

When I fell, I got a serious blow on the head.

I hit my head badly when I fell.

2. Unfortunately; Frustration; difficult

We have to suffer some blows in life.

We have to suffer some setbacks in life.

3. Knocking sound

Step 4 criticize, criticize