It was the cowards' way out, but right now she wasn't up to confronting him.
The Cornish knights (who in Arthurian romance are always represented as hopeless cowards), dare not contest his claim but Tristan challenges him to single combat, slays him and frees Cornwall from tribute.
"If I had answered your questions differently, I should have told a lie," said Otanes; "and none but cowards tell lies"
Only the defeated and deserters go to the wars, cowards that run away and enlist.
"It is disgraceful to run away from danger; only cowards are running away from Moscow," they were told.
They were ashamed to be called cowards, ashamed to leave, but still they left, knowing it had to be done.