He was three, and was mostly just being a toddler: he would get grumpy, get frustrated and yell when he couldn't do things, was making us tell him stuff dozens of times, over and over.

My responses felt reasonable at the time. Why wouldn't I get angry at him when he yelled at me? Oh, right, he's a toddler and I'm an adult. I've been in the saddle with respect to my emotions for decades. This could, no fooling, only be the 200th time he's ever been truly angry. I'm the responsible one here. Realizing I lost sight of that perspective was what took me by surprise and scared me a little.