1. The Unsanitized Label Injection: A developer instruments an API metric: ``http_requests_total{method="POST", path="/api/v1/users/12345/checkout"}``. Instead of grouping by the parameterized route template (``/api/v1/users/:id/checkout``), the raw user ID or transaction UUID is injected into the label. 2. The TSDB Index Churn: In Prometheus's Time-Series Database (TSDB), every unique combination of key-value label pairs creates an entirely new time-series stream. 50,000 unique customer IDs mean 50,000 separate in-memory series heads. 3. The Memory Avalanche: Prometheus maintains an in-memory inverted index of all active series. RAM consumption jumps from 4GB to 32GB in minutes. Compaction fails, WAL (Write-Ahead Log) replays stall on restart, and the entire monitoring node falls into an infinite crash loop.