The Latin phrase from common law is necessitas inducit privilegium quod jura privata ("Necessity induces a privilege because of a private right").
For example: In American law, the case most often cited to explain the privilege of private necessity is Vincent v. Lake Erie Transp.
To invoke the private necessity privilege, the defendant must have been actually threatened or have reasonably thought that a significant harm were about to occur.
The ruling in Vincent v. Lake Erie assures private citizens from a public policy standpoint that they will be compensated for their loss.
The decision in Surocco v. Geary differs from the private necessity doctrine that a trespasser must compensate a property owner for any damage she may cause.