Please humor me for a moment, and I think you will get my point.
Let's go on a visual journey together. Let's pretend you had one of those Murphy's Law kind of days. You know, if it can go wrong, it will. Pretend with me that your boss came to work grumpy and took it out on you. Someone posted a hateful comment on your Facebook paged, and some inconsiderate so and so cut you off in traffic, causing you to miss the green light, and now you're going to be late picking up the kids. You know what I'm talking about - one of those days that you wish you could have stayed in bed.
Now let's pretend that you make one last stop at the grocery store to pick up a few things before heading home, and it happens! Some jerk pulls in front of you and takes the only parking spot left.
At that moment, something inside of you snaps. You bang your fists on the steering wheel, rip off your sunglasses, step out of your car, and give that jerk a piece of your mind. All the while, your poor kids sit in the backseat of the vehicle, horrified, wondering if mom has gone crazy.
Mom's not crazy; she's Trigger Stacked. One adverse event during her day got stacked on top of the previous unfavorable event causing extreme stress. Think of it like the Straw That Broke The Camels Back kind of moment. On any other typical day, she might have been annoyed with the diver that took what she considered to be her parking spot, but she wouldn't have flown into the rage she demonstrated today - especially in front of her kids.
Trigger stacking can happen to dogs, just like with humans. When a reactive dog is Trigger Stacked he/she may lash out at others just like the mother did in our above story. Trigger Stacking can cause reactive dogs to pick a fight with another dog that is unlucky enough to be close by, even if that dog is their best friend or even their human family member.
Several events can cause Trigger stacking in dogs. One example is two reactive dogs behind a fence barking as people pass by. Soon a fight breaks out between the two dogs. When dogs are stressed, the body releases the cortisol hormone, which can cause the behavior commonly called flight-or-fight. When stress becomes a chronic problem, cortisol also causes issues, such as a weak immune system and other behavior issues. Somewhat like PDST in military personal.
It is essential to understand that just like you, your dog will encounter triggers during the day. The greater the number of triggers and the more negative the triggers are, for your dog, the more likely your dog's behavior of fighting will continue.