What makes Lego such an amazing, open-ended system?

Part of it is the lego dot; the way that all of the pieces fit together.

But that's not as important as it looks; there are a number of different dots that would have worked.

What's more important is the extremely tight levels of precision in the manufacturing process.

That's what allows every lego, even ones made decades ago, to fit perfectly with every other piece.

Each piece is inflexible and hard; but in combination the system has extraordinary flexibility.

The shape of the dot is arbitrary.

What matters is the precision.