Guilt.

One of the hardest things I've ever had to do was decided to sell my horse.

Having a horse was transformative for me. I knew nothing, bought a 6 month old filly, and had a painful, brilliant, amazing experience learning how to train her.
When I had to leave Washington State, where we lived, I should have left her there. But I had lost a lot of things, and I didn't want to give up one more. So I had her hauled across the country.
That's the part I really regret. Not actually selling her. I moved her to North Carolina, and sold her there, all the while wishing I had just left her in Washington with the people and horses she had lived her entire life with.

I hadn't really realized that this made me feel guilty. It was 100% the right thing to do to sell her and move away from North Carolina. But I felt guilty.

That guilt caught up with me. I was browsing various resources online for work when I came across the Animal Legal Defense Fund. They had on their website a campaign about a horse starvation case in North Carolina. And I was promptly launched into a anxiety attack when I saw this image (compared below, with a picture of the horse I had - the full effect diminished by one horse having a winter coat and the other having a spring one).
I left 10 minutes early to so I drive, like a madman, home to compare pictures. I convinced myself it wasn't her, only buy the left hind sock being a different height.
I promptly donated some money to ALDF, though. And it also prompted me to try to track down the people I had sold her to. I'll let you know how it goes.