Shiva is also referred to as triambaka because of his third eye - the eye of vision. on mahashivaratri, nature brings this possibility very close to us. while this is possible every day, on shivratri nature makes it more available to us because the planetary positions are such that the energy, especially in the northern hemisphere, makes it very easy for a person to raise his/her energies upward.
may you be blessed enough to become a triambaka on this auspicious day!
happy mahashivaratri!