Sharding is a popular feature in MongoDB used for distributing data across clusters for horizontal scaling, providing benefits such as scalability. However, adding complexity to a distributed system increases the chances of encountering common issues when moving to a sharded environment. Many of these problems can be mitigated if aware of best practices and situations to avoid. This blog series aims to provide cautionary tales about pitfalls and gotchas that MongoDB users have encountered, including shard key selection and changes, which are crucial for horizontal scaling. Choosing the right shard key is essential to avoid issues such as insert scalability limitations, while using a hash-based shard key can provide good write scalability. Additionally, sharding a previously unsharded collection requires careful consideration of updates to the shard key, where attempting to update it in-place may fail with an error. By understanding these pitfalls and mitigation strategies, MongoDB users can better navigate the challenges of sharding their environment.