Most legacy application modernization projects fail on two simple options: a full feature freeze, or shipping new work on both systems for as long as the rebuild takes. The rule that usually works is a short, dated freeze on the area being rebuilt. Agree in writing that new features go only on the new system once each part of it is live. If you are a CTO, you know this meeting. Sales has deals waiting on a feature. The old system gets more fragile with every release. Someone senior asks why t...