be on, show, prove, etc. your mettle
be on, show, prove, etc. your ˈmettlebe prepared to do the best work you can or perform as well as you can in a particular situation: When the boss comes round, I want you all to show your mettle. ♢ He’ll have to be on his mettle if he wants to win the next race.
Mettle is the ability and determination to do something successfully in spite of difficult conditions.
See also: mettle