I think that architects and developers often forget the basics software development when planning rewrites. Because they've been working on the product for so

I think that architects and developers often forget the basics software development when planning rewrites. Because they've been working on the product for so long, they think the normal rules of working iteratively and getting feedback don't apply. They try to replicate the entire existing system at a point in time, turning the rewrite into a waterfall project. Then they're surprised when things they fall behind and can't adjust. You're better off in almost all cases to break it up and approach the problem as refactoring instead. When I was an "e-business" consultant, we had a saying: "Six month projects take nine months, twelve month projects take eighteen months, and two year projects get canceled." If your rewrite is projected to take over a year, you're in huge trouble.