This reminds me of a React/Flux talk by Facebook's Jing Chen about how there were pieces of code within the product that literally nobody wanted to touch becaus

This reminds me of a React/Flux talk by Facebook's Jing Chen about how there were pieces of code within the product that literally nobody wanted to touch because they were so fragile and complex. I suspect there is something similarly messy in the PayPal business accounts, and for whatever reason a ground-up rewrite was also a challenge.