Exactly. And you don't always need a lot of traffic, so even if your code survives load testing doesn't mean it's correct. Just last week I ran into a serious problem with a piece of code that handled infrequent events from several different threads, and an almost unrelated refactoring changed timing so that events arrived from two different threads exactly at the same time, on exactly one family of Android phone models. The original mistake had been in production for a long time without anyone noticing.