The I Ching always seemed rather Rorschach-y. But that could be because I've seen suggestions that the popular Wilhelm/Baynes translation is rather Westernised and some way from the original meanings.
It's probably like trying to make sense of Shakespeare if you grew up in China and didn't start learning English until you were an adult. The language isn't just poetic - it's metaphorical, idiomatic, and allusive, and it's probably impossible for non-natives to truly understand it.
For him, it worked out terribly, in the sense of pushing closer to a psychotic state.
From that experience, it's hard for me appreciate the poetic vagueness of this stuff given that same poetic vagueness helps sell Western Astrology.
[1] - https://www.amazon.com/Dice-Man-Luke-Rhinehart/dp/0879518642
Psychosis and mystical experience are after all closely linked if not objectively identical.
The Yijing, when used properly (as a tool for self-exploration and psychonautics and not for fortunetelling or the chasing of idle fantasies) works similarly to the Tarot or other symbolic systems that operate on the human psyche. There comes a point (with repeated use and appropriate conditioning/reinforcement) that these systems really open up the subconscious and can lead to mystical unions or profound annihilatory experiences (ego death).
So it sounds to me that your friend had no idea about these things and simply could not handle the "results". When you play with fire, you take precautions or you get burned..
He had a theoretical understanding of "ego death" and perhaps he experienced that.
That problem is that none of this quite had a cut-and-dried, desirable effect. He didn't reach the final stage like Friedrich Nietzsche - no wait, he kind of reached the final stage more or less like Nietzsche.
I also consulted it about a possible career change I was contemplating. The result talked about revolution. It seemed a rather pertinent result for the question at least. I did not end up making that particular career change. Perhaps the I-ching poems persuaded me not to make the change, because they talked about how a revolution is a very grave matter that must be attempted only in dire circumstances.
Randomly.
"One could say that the I Ching is a mirror of one’s own concerns or expectations.
feed a random signal in then examine the outputs. Results will tell you something about the dynamics of the system that processes the signal.
"But it’s like one of the bronze mirrors from the Shang dynasty, now covered in a dark blue-green patina so that it doesn’t reflect at all."
Perhaps the input signal from the hexagrams relates to a culture so remote from the modern world that it tells us little about ourselves now.