"Gazing into an abyss" is a metaphysical concept that has nothing to do with looking into a physical abyss of any sort. It has to do with any abyss from the spiritual to the Constitutional to fiscal responsibility to wondering if we are alone in the universe.
Take the last example. If you stare into that one long enough, and throw in an unhealthy dose of spiritual loneliness for intelligent, warmhearted, cosmic neighbors, the abyss will turn and become part of you. It won't really be gazing back into you. But you will have created a mirror in your mind that will swallow you. Human companionship won't be enough anymore even though it is the only option so far as creatures of reason are concerned.
One of my favorite books is The Immense Journey, by Loren Eiseley. My favorite passage in that book is the part the title comes from:
"For the first time in four billion years a living creature had contemplated himself and heard with a sudden, an accountable loneliness, the whisper of the wind in the night reeds. Perhaps he knew, there in the grass by the still waters, that he had before him an immense journey. Perhaps that same foreboding still troubles the hearts of those who walk out of a crowded room and stare with relief in the abyss of space so long as there is a star to be seen twinkling across those miles of emptiness."
Staring into the abyss creates "foreboding". The abyss of the people who feel relief by walking out of a crowded room is probably in the emptiness of the people they escape from by walking out to look up into the sky. For them, the abyss is not a sorrowful need for cosmic company, but a real spiritual need for company right here on earth that isn't hollow, empty of values, or looking for a self-aggrandizing pat on the back. They stare into the abyss of space as a relief against the immense journey they know that man has yet to travel to be the creature he ought to be.
For those who walk out those crowded rooms after gazing into the abyss of the spectacle of small-minded, shallow, grab-what-you-can people, they leave the abyss behind them. To stay and become one of those people means you have fallen into the rabbit hole, and that hole is the abyss staring back at you.