Great point about using business metrics to notice real customer problems, but when you have to find out _why_ those metrics are off, logging is helpful. This

Great point about using business metrics to notice real customer problems, but when you have to find out _why_ those metrics are off, logging is helpful. This reeks of functional programmer brain. The world is not immutable. the world is weird. Your systems will interact with other systems that don't always quite work. Sometimes, their systems are wrong, or update without your knowledge, or theres other issues in routing, networking and whatever else. Logging errors like "I can't resolve this domain" is more helpful than "my customers can't use this integration and business is at zero"