The definite article is used for specific things. In the following sentence the noun "disappearance" is not specific (no one is missing):
The disappearance of a person cannot go unnoticed .
Why is the definite article used here?
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"Disappearance" is not indefinite. It is abstract. "Disappearance" represents one of many types of condition or state that relate to a person such as presence, absence, health, etc.
The absence of a prisoner is supposed to be noticed by the guards.
The doctor said that the health of patients is the only responsibility of a physician.
I think you are confusing indefinite with abstract. The abstract does not specify an individual, to be sure, but a specific abstraction can be distinguished from other abstractions.