Because more often than not, people don’t.
They way I grew up with agile, one of the basic tenets of all agile approaches was the notion that there is no prescribed ‘right’ process, but you have to do what it right at this point in time. There even was a lengthy discussion whether the approach should be called ‘agile’ or ‘adaptive’ when the agile manifesto was created.
Now I see people ‘doing agile’ all around in manners I sometimes fail to understand. And I hear complaints that the agile stuff doesn’t really work. And more often than not, the explanation I get is along the lines of “But agile says ‘inspect and adapt’ and we adapted.”
And what I see quite often when I hear that teams ‘adapted’ the approach they try to use, is exactly that – they adapt without doing the inspection of the real thing first. Go ahead - read it! :)
So if you want to use the inspect and adapt approach, please make sure that you have something to inspect before you adapt it.
till next time