Explanation
The seconds before the point arrives are the seconds during which people leave, and almost every underperforming video has a measurable gap between when it started and when it began. Counting that gap and comparing it against the retention drop usually shows the same number twice.
In practice a cold open means deleting the first sentence you wrote. Introductions feel necessary to the person who made the video and are invisible to a viewer who has no context and no obligation to acquire any.
The common mistake
Confusing a cold open with skipping the subject. Starting mid-action still requires naming what is happening, because a viewer who cannot tell what they are looking at leaves faster than one who was mildly bored.