This is also the reason massive software rewrites often fail; you rebuild the general gist quite fast, nice code, lovely interfaces etc but it will have a trillion bugs which come from decades of adding an exception here, adding one there etc. So now you have a beautiful albeit worthless product. And often these get scrapped: I know of some tax system rewrites from mainframe to modern code that costed 10s of millions and were scrapped, multiple times for this reason.
