Over the course of a large Drupal site's existence, many hands contribute to the work, and teams come and go: the agencies that helped stand the site up may not be the ones maintaining it, and the developers later brought in or update or expand upon the site probably had no influence in its initial build. Moreover, the folks tasked with owning the business performance of the site may little to no understanding of why the site is the way it is, and why things just can't be better. 

From the perspective of the site owner, it can all feel like an endless pit of concern, shortcomings and expense. And on top of this all, the Drupal site is a secondary concern to their primary goal of running a business! It's little wonder then that there are entire businesses based around the concept of 'rescue' or 'ongoing support' development efforts, which inevitably lead to hard-reset rebuilds when the mountain of technical debt becomes insurmountable.

What does it truly take to build a Drupal site (or suite of sites!) that can sustain a business in the long term, especially if you're not primarily in the business of making web sites? What can you expect to deal with over the years? How can we avoid the painful and self-destructive cycles of build, fail, rebuild, repeat -- and what can developers and the Drupal project itself learn from this cycle?