Fault tolerance is a critical aspect of modern application architecture, designed to ensure systems continue operating smoothly in the face of errors or outages, thereby preventing loss of functionality and maintaining customer confidence. The article highlights the significance of fault tolerance by contrasting it with high availability, emphasizing that while related, the two are not synonymous. It explores different strategies for building fault-tolerant systems, such as using multiple hardware systems, software instances, and backup power sources. The piece also discusses the balance between normal functioning and graceful degradation, as well as setting survival goals to determine the level of fault tolerance needed. Financial implications are addressed, noting that while fault-tolerant architectures can be costly, the expenses of outages, including revenue loss, reputation damage, and team morale impacts, can be even greater. Real-world examples, such as a major electronics company's decision to migrate to CockroachDB for enhanced scalability and reduced labor costs, illustrate the practical application of these concepts. Overall, the article underscores the importance of thoughtfully architecting systems to withstand various levels of failure, thereby ensuring operational resilience and efficiency.