Joel Spolsky has a pretty good rundown. The biggest takeaway for me was that legacy apps usually don't have clear reproducible requirements. All the corner cases are written down in one place: the old code. Throwing that out means you'll recreate most of the bugs that were already fixed in the old system.
It is painful to look at and work with the old code, so we want to avoid it. But some things worth doing are painful, like exercise, or getting a cavity filled.
It is painful to look at and work with the old code, so we want to avoid it. But some things worth doing are painful, like exercise, or getting a cavity filled.
[edit] https://www.joelonsoftware.com/2000/04/06/things-you-should-...