I think I'd rephrase that to: The company that's going to put you out of business is using an early version of their own legacy code. It's not always obvious

I think I'd rephrase that to: The company that's going to put you out of business is using an early version of their own legacy code. It's not always obvious when you should attempt a rewrite from scratch. Having done a few refactorings, I've noticed one desirable trait in good code bases: If you can implement new logic easily in a few lines of code, it's probably a good design. But if you need to get out the surgeon's knife and write tons of new code every time you want to implement new logic, it might be fundamentally flawed enough to warrant a complete rewrite. A good design is adaptable and will allow you to be resilient against newcomers.