limitation
This word carries a sense of a boundary or a ceiling that cannot be crossed. It often suggests a frustration or a constraint imposed by external rules, laws, or physical laws of nature. It is frequently used in professional or technical contexts to define the scope of a project or the capacity of a machine. When applied to people, it shifts toward a tone of humility or realism. It describes the edge of one's competence or strength. While a restriction is often an active rule, a limitation is often an inherent property or a fixed reality that must be accepted.
Countable when referring to a specific rule or a particular weakness (three limitations of the study). Uncountable when referring to the general state of being restricted (a life of limitation).