Scaling Out MongoDB: Understanding the Fundamentals of Scaling an Application` As an application takes off, it's essential to consider why it's scaling and what issues may arise down the road. This includes understanding the workload characteristics, such as read-heavy or write-heavy operations, and identifying potential bottlenecks caused by factors like bad schema decisions, inefficient indexing, or insufficient resources. When deciding whether to scale horizontally or vertically, it's crucial to weigh the trade-offs between these approaches, considering factors like hardware upgrades, disk speed, and network latency. Choosing a shard key wisely is also critical, as it impacts performance and can lead to common sharding pitfalls if not selected carefully. By taking advantage of MongoDB resources and expert guidance, developers can make informed decisions about scaling strategies for their applications.