The saying "in broad daylight" likely comes from the simple fact that it is easier to see and be seen in the light of day, making criminal activity more difficult to carry out.

Here's how it likely evolved:

* Literal Meaning: The phrase literally describes a time when there is abundant sunlight, allowing for clear visibility.

* Metaphorical Extension: Over time, the phrase shifted to describe situations where something unexpected, shocking, or even illegal happens in an obvious or unconcealed manner. This is because it would be highly unusual for such events to occur in broad daylight, where they are easily witnessed by many.

* Emphasis on Boldness: The saying implies that the act is done with audacity and without fear of being caught, much like a crime committed in the open when everyone can see.

In summary, "in broad daylight" is a saying that highlights the contrast between the obvious nature of an action and the usual expectations of darkness or secrecy surrounding such events.