Reality is fundamentally structured by constraints: exclusions that define what can exist, persist, and transform. Systems remain stable when constraints are mutually satisfied, but necessarily encounter generative limits where local admissibility produces global incompatibility, forcing reorganization rather than incremental change. This dynamic explains patterns across domains: paradigm shifts in science, evolutionary novelty, cognitive restructuring, and phase transitions all reflect the same underlying mechanism. Constraints explain persistence through exclusion while generative limits explain transformation through necessitated reconfiguration, forming a self-anchoring ontology where intelligibility, change, and novelty arise as structural consequences.