Noun
moral fibre (usually uncountable, plural moral fibres)
(UK) The inner strength to do what one believes to be right; often an ability to make difficult decisions.
He lacked the moral fibre to be a leader.
[re Princess Diana's death] I wondered at the time, what had happened to the moral fibre of the island race - the stiff upper lip, if you like - to make them behave like professional mourners howling for hire. The Prime Minister was proud. I was ashamed. George MacDonald Fraser
Life is made too easy. Mankind's moral fibre is giving way under the softening influence of luxury. Johan Huizinga