Parenting

I think a partial mistake is just too much for them to process, so their toddler brain would rather finish whatever behavior they started, then figure out what to do next.

Toddler brain: "Oh, I'm spilling my drink... Better spill it all the way, because we need to clean it all off of the floor."

Adults and even animals do this too. It's a response to frustration. It's what's behind the "tear it down and rebuild it again from scratch" mindset. It stems from perfectionism and neuroticism. A good rule to teach kids is that mistakes are acceptable and nothing will ever be perfect. An existing partially good result is preferable than an inexistent perfect result. Enjoy and trust the process, ignore results for a while, learn from mistakes.

It's also related to tolerance and flexibility. For example, some people find it intolerable to dirty up or scuff a newly bought item, let's say a new car or new phone. Being overtly careful or even refusing to use it at all to avoid damage (how people also avoid doing things they fear they will fail at or be embarrassed). But come the first scratch, you now have to live with it. To survive the emotional response to frustration, our brain drops expectations and sometimes overcompensates exciting our aggression impulse.

This is why we recommend people certain exercises of pure exposition to frustration. Like those theater exercises that make you act ridiculous in front of the class, or thought dumping to get rid of writer's block, or doodling to break in a new sketchbook. It's like recalibrating emotional responses to be more flexible and tolerant of imperfections. To get comfortable with discomfort and learn to bounce back from failure.

Funny, I can feel the feelings of this urge, as I read. (Disclaimer: I am not actually a toddler.)

I can't dissect my feelings fully, but I think a large part is feeling the anticipation of shame/failure from the whole thing going wrong (e.g. the whole cup of dog food falling out) and as long as you haven't completed the task, that threat stays there. Spilling a few pieces draws attention to that threat - presumably to warn yourself off it. Throwing the whole thing down gives a wonderful relief: there is no more threat, no more striving for what might not be; what's done is done. But after that, with the stress gone and the relief come, you feel the clearness to start again.

Okay I have a sudden thought.

You know how sometimes you'll be, say, walking over a bridge, and your brain will say "YEET YOUR PHONE INTO THE RIVER!" And you're like "Fuck no, why would I do that?" and you stick your phone in your pocket and move away from the railing?

Call of the void. I'm convinced that this is your primitive brain's way of reminding you what not to do by creating "dangerous" situations for you to respond to in the appropriate way, because we just don't run into dangerous situations like that very often in modern societies.

Extending from that, I think that there's a time in young children where their brains have advanced to be able to do the "call of the void" thing, maybe triggered by an accident with dog food or a bottle of water, but haven't advanced to where they don't answer that call.

All of the above is constructed out of pure speculation. But it sounds good to me.