1. He's bigger than any of my other horses and wears the same size clothes as my dearly departed gelding. Now those clothes won't go to waste! (Only problem with that is my other guy's color was blue and River is pink, but even I can't justify getting a whole new wardrobe for that reason. Not at all once, anyway...)
2. Name pattern. Every horse I've owned or cared about has has an "i" as the first vowel in their name: Chip, Striker, Irish, Riley, Wilson, Lily, now River. What are the odds? It was meant to be.
3. He has the same birthday as one of my sisters. Of course, said sister isn't a horse person and no one in my family knows about River, but...
4. It just worked. Lots of things could have gone wrong; if I wasn't meant to have him, I wouldn't have been able to.
I'm not actually a big believer in fate, but sometimes it's easier to trust it than think about what you're doing.