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+To do that let's look at how architectural evolution
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+occurs in practice. Ideally when a system evolves, its prescriptive
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+architecture should be modified first. Just like when you
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+modify a building. You change the blueprint and then you
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+change the actual building. You don't go the other
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+way around. In software, unfortunately this rarely ever happens in
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+practice. In practice the system, and therefore it's descriptive
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+architecture are often directly modified. Like in this case that
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+I'm showing here. So what happens is that the architecture
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+as conceived does not change. Whereas the architecture as implemented, does
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+change. And therefore these two things start diverging. And this really
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+happens for a number of reasons. So I'm just going to list
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+a few of those reasons here. In some cases it
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+just happens for plain sloppiness. I need to make this modification
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+and I don't really want to go back and look at
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+the prescriptive architecture modified. I'm just going to make the change, and
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+maybe I'll fix the description later. And then you never really get
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+to it. In other cases you do this because of the perception
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+of short deadlines. If you have to do something by this afternoon,
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+you're not going through a four
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+month software architecture review, you normally just
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+get to it, and do it. In some cases a prescriptive architecture
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+is not even present, so there's a lack of documentation. So in these
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+cases, clearly, you cannot go and modify something that does not even
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+exist, and so you jump directly to the code and start modifying that.
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+And as I said there's many, many more
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+other reasons why that happen. But important point here is
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+that it does happen and it does happen often
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+and the result is that prescriptive and descriptive architectures diverge.