Rav Kook writes that midas HaYesod can bring a person to a lower level than he really is at, and the opposite is true as well, it can boost a person to a higher level than he really is, as the Pasuk says "Tzaddik bechol hadoros" (meaning that a Tzadik, i.e. one who guards the bris, is considered a Tzadik in all generations, not just in his).