Someone says it is because in the past the heavy labor of blacksmiths had weakened their one eye and one leg; other says it is because Ippon-datara had appeared near the remains of mines (refer to myths of single eye and single eye in legends).
これは鍛冶師が重労働で片目と片脚が萎えること、一本だたらの出没場所が鉱山跡に近いことに関連するとの説がある（隻眼神話・伝説の中の隻眼を参照）。