It is great when products reach product market fit but if their architecture doesn’t enable them to onboard and service customers effectively, those companies will not able to scale their business beyond the few handful customers.
Sometimes, a rewrite of the core product is called for to accomodate the business requirements from a fresh perspective. In such cases, the technical effort is akin to replacing the engine of a airplane in flight, because neither the customers nor the competition is waiting for you to catch up.
Read more on the experience working on such an effort on the Sahaj engineering blog