It all starts with chicks. You see, chicks are fuzzy and so is the subsequent chicken math.
 
It's like when you have a conversation regarding chickens with your significant other.
"Honey, can I get some chicks?"
grumble grumble...
"How many? Is 6 chicks too many?"
grumble grumble grumble...
"Honey, I just got home from the feed store with our new 9 baby chicks!"
Ack. GROBBLE grumble ick!
"But these other 3 were so lonely in their own pen and they looked like they wanted company..."
SO shakes head understanding that this battle was lost.
 
A few months later.
SO: "Why are there more than 9 chicks in the run now?"
Oh, I was at the feed store and someone was wanting to return their chicks but they were too old so they were going to dump them. I couldn't let that happen so I brought them home. See, if you hadn't counted you wouldn't have known there were more.
SO resigns self to another defeat.
 
A year later...
SO "Dear, why was there an incubator box shoved way deep in the garbage can? It was like it was hidden."
The guilty party: "An incubator box? I don't know anything about it."
 
A few weeks later.
SO "Dear, I am hearing peeping from the tool shed. Is there something that I should know?"
 
In a nutshell, that is chicken math.
We all start with a modest amount. And it grows. And grows. And when you want it to stop, they little buggers will hatch their own for you.
 
ETA:
I started with 8 little red sex link chicks. They were to go into their own little tractor and provide us with fresh eggs. I quickly learned that 8 cute little chicks can devastate the ground under a tractor in a couple of days. Hence came run #1. I then found some local Silver Sebrights (5) and White Rocks (5). Hence came run #2. White Rocks will go broody and so will my red sex links. Three weeks later another 13 chicks were bestowed upon us.
 
Then came the incubator.... I ended up with well over 100 at the peak. I had chicks and chickens in every nook and cranny that I could find.