(idiomatic) The survival of the fittest, strongest, or most cunning

(uncommon) Alternative form of when in Rome, do as the Romans do

(idiomatic) To maintain one's concentration fixed on one important theme.

(idiomatic, US) To perform actions consistent with one's claims.

(idiomatic) To work especially hard, usually for an extended period.

(colloquial) To make a show of bravery despite one's fears; to put on a brave face. / (idiomatic, US) To speak of something despite having little knowledge of it.

(idiomatic, US) To attempt to stay cheerful in a dire situation; to proceed with a task, ignoring an upcoming hazard, hoping for a good outcome.

(idiomatic) An attestation to the truthfulness and frankness of an associated statement.

The world, a place where darkness and death are figurative valleys one must walk through as part of the human experience. / A very dangerous place.

Alternative form of hold the cards