In the famous Greek myth, Princess Ariadne helps Theseus negotiate the Minotaur’s maze by giving him a ball of thread so he could backtrack if he got lost.
The phrase “Ariadne’s Thread” refers to to the problem-solving technique of keeping a meticulous record of each step taken, so that you can always backtrack and try alternatives if your first efforts fail to yield results.
It’s a useful metaphor for understanding the tedious task of challenging DNA evidence. You have to backtrack, note dead ends, attempt iterations that may not yield results, then try again.