What is the root of bitcoin? What makes it revolutionary at the core?

I see a lot of posts asking how one can explain this to their friends and family in the simplest way possible. This is my take:

It automated double entry bookeeping, allowing math instead of people to be trusted for it.

Double entry was a really cool invention which paved the way for the modern world.

Edit:

The central idea im getting at is that this is the first time in history we dont have to trust people (a notorious weak link), but can trust something infallible instead - math