When building resilient, fault-tolerant, scalable systems, we focus quite a bit on the particular technologies involved. Can they scale horizontally? Is Samza better than Storm? Is this library thread-safe? It turns out that even though those questions matter to the stability of the system, they aren’t as important as the people building the system. Humans choose the stack, write the code, and write the bugs, too. They create the weird edge cases that cause the system to fall over at the worst time.