It's more accurate to say we grew them. That is the breakthrough of Deep Learning. We left the hard part to the machine (learning how to do what you want it to do) to figure out during training.

And that means we are not privy to whatever things it has learnt in its trillions of weights.

https://xkcd.com/1838/

We might have built them, we sure as hell didn't design them. And no, we do not have a decent idea about how it works.