Scientists must account for unknown quantities when modeling climate systems.

Every Remembrance Day, citizens place flowers at the tomb of the Unknown Soldier to honor those who died unidentified in war.

Managers often ignore the unknown known — a certainty of unknown magnitude, consequence, structure, and probability characteristics that nonetheless shapes outcomes.

During the safety review, the team treated the equipment's remaining variability as a known unknown, documenting its magnitude, likely consequences, and probabilistic structure.

In the audit, we discovered several unknown knowns that had quietly influenced our decisions.

In planning the mission, the team catalogued the known unknowns and prioritized their investigation.

The experiment revealed an as-yet-unknown that challenged existing theories.

Scientists are still grappling with several as-yet-unknowns in the data.

The as yet unknown cause of the malfunction has puzzled the engineers.

The as-yet-unknown risks associated with the procedure worried the medical team.