alt Hacker NewsLife lesson for you: the internal functions of every individual's mind are unique. Your n=1 perspective is in no way representative of how humans as a category experience the world.
Plenty of humans do use longhand arithmetic methods in their heads. There's an entire universe of mental arithmetic methods. I use a geometric process because my brain likes problems to fit into a spatial graph instead of an imaginary sheet of paper.
Claiming you've not examined your own mental machinery is... concerning. Introspection is an important part of human psychological development. Like any machine, you will learn to use your brain better if you take a peek under the hood.
> Claiming you've not examined your own mental machinery is... concerning
The example was carefully chosen. I can introspect how I calculate 356*532. But I can't introspect how I calculate 14+17 or 1+3. I can deliberate the question 14+17 more carefully, switching from "system 1" to "system 2" thinking (yes, I'm aware that that's a flawed theory), but that's not how I'd normally solve it. Similarly I can describe to you how I can count six eggs in a row, I can't describe to you how I count three eggs in a row. Sure, I know I'm subitizing, but that's just putting a word on "I know how many are there without conscious effort". And without conscious effort I can't introspect it. I can switch to a process I can introspect, but that's not at all the same