In a recently reported issue with an Apple Car almost running over a pedestrian, someone on HN asked why can't we simply add the code:
if (personInFrontOfCar) { halt(); }
The reason, of course, is the self-driving algorithms are all done with machine learning. The model is trained with a corpus of information and the result is a "black box." The programmer could not insert the above `if` statement if they wanted to, they could not modify the source code of the model as if it was normal business logic. Instead, they would have to re-train the model on new data.
This is what people mean when they say it is a "black box." There is no source code to edit, only training data that outputs an as-is model. It's similar to getting binary blobs, for eg Linux drivers.
In contrast, I could fork regex if I wanted and add an `if` statement in the middle of it, and re-compile it. It is pure source code. Same with grep.