CIA triad
Confidentiality, integrity, availability. Lose one and the system is already failing, even if the dashboard is green.
Three properties, not a slogan. Confidentiality: only authorised people and services see the data. Integrity: it was written, changed, or deleted by someone allowed to. Availability: it is there when authorised work needs it.
Ransomware punches all three. A quiet edit of a payroll file is integrity. A flood that takes the site down is availability. A dumped backup is confidentiality.
Use the triad as a check on every control. If a spend does not serve one of the three, it is decoration.
Fact source: ASD's ACSC glossary.