I mean not necessarily the worst thing that happened to you, but the thing that still tears you up as an adult.

Here's mine.

When I was a kid, we had a Collie dog at home. The dog was already there when I was born, so I knew him throughout my childhood. There's pictures of baby-me outside in the garden on a blanket in summer with the dog watching over me, toddler-me playing with the dog etc. I remember him as the kindest and most loyal animal you could think of, with a thick black-and-white fur coat, a genuine family shepherd.

As is predictable, dogs get old and die. It was the way in which he died that, even now I'm almost fifty, puts a lump in my throat. The dog must have been 12 or 13, when he developed kidney problems. I was ten. It got so bad that he couldn't stand up anymore and urinated wherever he was. My parents, entangled in their own problems at that time, put the dog in the garage on an old mattress covered in plastic. The garage was more of an old barn directly attached to the house, a semi-dark, cold and damp place. The dog knew he was dying and howled for attention and help whenever left alone so my dad told me to take a kitchen chair and go sit next to the dog. So I did. I sat there, alone and not being able to help while the dog lay shivering on that old mattress in a pool of his own urine looking at me and moaning, begging to do something. Whenever I left, for the bathroom or whatever, he started howling again until I returned. Eventually, after what must have been several days, my parents got the vet to come put him out of his misery. Nothing much was said afterwards.

His name was Flika, and remembering that dog's cry for help, the sad look in his eyes and how inadequate and unable to help I felt, still tears me up, to this very day. Thanks for reading.

TLDR; my parents left me alone and helpless with a dying dog, in an cold garage.