Distance-based algorithms—such as K-Nearest Neighbors (KNN), K-Means clustering, and many similarity-based models—are foundational pillars in modern machine learning pipelines. However, a pervasive but often underappreciated threat undermines their reliability in real-world data: unscaled features with varying magnitudes. This problem can fundamentally distort analyses, result in misleading clusters or classification boundaries, and greatly reduce the interpretability and
High cardinality features—categorical variables with a large number of unique values—can turn otherwise manageable datasets into a dimensionality nightmare, overwhelming machine learning pipelines, exploding memory usage, and degrading model performance. This problem is central in contexts ranging from web event logs and retail transactions to medical records and observability data in modern distributed systems. What is
Target leakage—particularly via premature or improper feature creation—remains one of the most insidious causes of model failure in machine learning. When features encode information that is unavailable at prediction time, or when they are constructed using data only accessible post-hoc, models become unrealistically accurate during development and disastrously unreliable in deployment. What Is Target Leakage?