i mostly am familiar with network side of things, but little stuff like how you handle connection timeouts or retries, for example, make a really big difference to the overall quality of the system. Not thinking about a network call each time is setting up a system that will randomly fail in avoidable ways (excessive retries keeping a system from recoverying; excessive buffering in the face of latency; unbounded memory queues causing failure propagatin; having best effort code handle connect failure quickly but not have good rear time outs, etc)

The higher level problems often emerge from the exact nature of the lower levels.