When I have seen large rewrites fail, it's often because of an all-or-nothing rather than iterative or staged approach. At my previous company, 2 different mana

When I have seen large rewrites fail, it's often because of an all-or-nothing rather than iterative or staged approach. At my previous company, 2 different managers approached the migration of a massive VB6 project. The first tried a total rewrite in C#. The code was ingenious and better in many ways, but ultimately it failed after many wasted man-years, and he was let-go. There was just too much hidden wisdom in the spaghetti code to replace it quickly and easily. A wiser manager, and friend of mine, managed the rewrite, but in stages. He would carve out a chunk, and have it replaced. He's a director there now.