Developing applications with resiliency as an important factor always makes your customers happy. Today, applications are distributed by nature and involve lots of communication over the wire. Problems arise when the service is down or not responding on time due to network failure, which eventually leads to a delay before the client operation is terminated. The purpose of resiliency is to make your application recover from a failure and make it responsive again.
Complexity increases when you call one service and that service calls another service, and so on. In a long chain of operations, considering resiliency is important. This is the reason it is one of the most widely adopted principles in microservice architecture.