grit
grit your teeth make a great effort to keep your resolve when faced with an unpleasant or painful duty.
2012Daily Telegraph The former French minister of finance lives her life according to the advice of her former synchronised swimming coach: 'When it's tough, grit your teeth and smile.'
true grit strength of character; stamina. informal
☞ Grit in this colloquial sense originated in early 19th-century US English. True Grit was the title of a 1969 Western starring John Wayne.