StephanosGnomon: "...any number of substances can turn a normal, intelligent individual into a person who commits incredibly foolish and dangerous actions...."
Sometimes substances don't even have to be involved.
Many years ago, when I was young and stupid, I was involved with a woman who was just... whew! Our relationship finally ended when I had her arrested for domestic violence, after she had gone "Play Misty For Me" on my house and my person for the fifth time. She attacked the arresting officers in my front yard as they led her, handcuffed, to the cruiser, kicking one and headbutting the other. The female cop coldcocked her with a Maglite, driving her to her knees, and they put her in the cruiser--more gently than she deserved, I think. Pretty stupid.
Anyway, that was the fifth time. The fourth time, I put a gun on her: a .357 Magnum loaded with hollowpoints. I was aiming at her thigh, but I would never bluff with a gun and it's the only time I've ever pointed one at another human being. I fully intended to fire unless she stopped right then and there. She stopped, thank God. That gun with that ammo probably would have blown her leg off.
I was not drunk, high, or anything else (neither was she). I was simply angry beyond all telling. That's how stupid we can become in a moment of rage. I still shudder to think how close I came to crippling--or even possibly killing--someone.
It only takes a split second for someone to fuck up his life.
She's dead now, incidentally. She died peacefully in her sleep when a brain aneurysm burst, years after the last time I saw her. When I learned of that through a mutual acquaintance, my acquaintance seemed shocked that I sounded so blasé about it. "You don't sound surprised," she said.
"Honestly," I replied, "the only thing that surprises me is that she went from natural causes."
Since then, I have wondered if the aneurysm wasn't there all along, making her nuts.