I know of a company that was pretty successful with a VB6 app they wrote in the late 90s, but twenty years later they needed to modernize. They spent two years

I know of a company that was pretty successful with a VB6 app they wrote in the late 90s, but twenty years later they needed to modernize. They spent two years on a from scratch rewrite that was never completed (second system syndrome). The company abandoned the rewrite, acquired a competitor, and rebranded it as the company's new product. It turns out the competitor's code base had serious deficiencies (couldn't scale to the company's size, had important bugs), and was very unpleasant to develop against. In the 6 months following the acquisition, well over half of the engineering team left the company (heavily skewed towards the highest-caliber engineers) because they couldn't stand what their jobs had become. Many long-time customers threatened to leave because of user facing technical issues in the acquired product. A telling incident: the company needed to deploy an emergency fix to the mobile app. The only machine authorized to publish to the app store was a laptop that the owner of the acquired company had left at home overseas. To complete the deploy, he needed to call his wife and walk her through the publication process over the phone. The company managed to fix enough of the problems that they're still around today, but for a while there was a lot of uncertainty around the company's future.