I would guess that the #1 question that I’m asked — the top situation that people want resources for — is what to do when your child has already tilted past the threshold of 100% dysregulation and is melting down, right now.
I’ve answered that one in my post called Survive about as well as it can be answered (and I can put it in the comments for anybody wondering).
This is one step back from that. But I still feel like it’s a valuable model for understanding what happens when you hit that 100% dysregulated point.
So, here’s my pitch: there are “straws”, and there are “slaps”.
Obviously human emotional processing can’t actually be boiled down into a system of numbers. But for a moment, let’s pretend it can. Let’s say that a “straw” is something that is 1% dysregulating, and that a “slap” is 90% dysregulating, and that when a person gets 100% dysregulated, they melt down, no matter what.
So if anyone experiences a “slap” then they are overwhelmingly likely going to tip into full dysregulation. That’s why it’s named a “slap”; for most people, on most days, being randomly slapped would probably make them dysregulated — maybe anxious, angry, hurt, insulted. Unless they’re already having a wonderfully regulated day and they’re less than 10% dysregulated when this event happens, most of the time, they’re going to become fully dysregulated.
A “slap” is not only a literal slap. This is a category for anything that happens that’s often 90% dysregulating.
Then there are “straws”. Named after the straw that broke the camel’s back. There were other straws on there, too, not just the one — but that one, even only 1% dysregulating, was enough to cause a tip into full dysregulation if it was paired with a day of 99% other dysregulating things.
On a good day, most people can probably handle a lot of straws before they hit that breaking point. On a bad day, even one straw could be what breaks them.

Why I think this can be helpful even with the question of “what do I do when my kid is 100% dysregulated” is because knowing whether your kid’s full dysregulation seems to be coming from straws or slaps is really valuable information.
If you notice that every day’s meltdowns are coming from a pile of straws:
You might be able to dig down into the pile of straw and find out which, if any, you can mitigate, remove, or change.
Sensory overwhelm might contribute straws. Chronic fatigue or illness might contribute straws.
I’ve written before about “the sensory weight of disability”, when I couldn’t walk — how even things like which utensil I was getting with my food, or which pillow for propping when I asked, might feel like straws, and the social guilt of not appreciating them enough was yet another straw, and the frustration with inability to just get it myself was yet another one!
Social interactions might be straws. Demands might be straws.

(Any of these straws could also be slaps depending on the human experiencing them; I’m not intending to label the size of these experiences, just give a variety of different sources they might come from.)
And then there might be situations with a mixture of straws and slaps. Maybe straws build up to 50% dysregulated every day and then a slap lands sometime in the rest of the day, pushing someone over the edge. That slap may or may not be fixable, avoidable; sometimes triggers are really hard or even impossible for someone else to fix. (Think of a “slap” like: sometimes the video game takes time to load, and the waiting experience is too jarring. It’s not always adult-imposed, demanding, or parenting-related.) Maybe you can’t make sure slaps from life never happen, but you can reduce some or all of the straws that take place, leaving more capacity for those big dysregulating events to happen without tipping over the edge.
Because it’s also possible to reduce dysregulation. The things people seek when they’re 100% dysregulated (crying, screaming, running, hitting, throwing things, shutting down etc) are clues for us as to what would help that person reduce dysregulation when they’re NOT 100% dysregulated, too. If you have someone who’s at 50% dysregulated because of an array of straws, you can start taking dysregulation back down. Maybe in some circumstances you reduce it all the way to 5% — a slap hits — and they’re not so activated they tip over to 100%.

Because of course, in real life, everything isn’t either 1 or 90. There’s a lot of nuance in play that this hypothetical reduces to flatter than it actually is. Some days everything feels like a slap. Some days everything feels like a straw. Some days you don’t wake up back at 0. Some straws are 5 or 10 instead of 1. Some slaps are 50 or 75 instead of 90. All of this could have increasingly fractalling complexity the more and more granularly I describe it.
Maybe just start here. Notice whether the next meltdown comes from a slap (“they just went from 0-100 with no in between!”) or a straw (“I could tell we were building toward a meltdown but I couldn’t head it off”). Then start noticing if the slaps are all the same, if the straws fit into a category. Maybe that will direct your problem-solving in a new way you haven’t explored before.