A shared dying last words (spoilers Everything)

"I wish you good fortune in the wars to come". An odd choice of words for any person facing a dangerous situation. This exact phrase was said by two characters of a completely different storyline, region and era of westeros. Arthur Dayne and Mance Rayder both say this phrase before they die. Other than this exact phrase there is nothing that is obviously common between them. If everything is done for a reason, then what could it be for these completely unrelated characters to share a dying phrase?

Edit: correcting autocorrect of names