tiny boy upstairs on the bus

yesterday morning I went for a short ride on the double-decker bus - went upstairs as I pretty much still do whenever possible, and there in the front row at the huge flat picture windows out onto the city, on the left, was a tiny little boy, the size one generally doesn't see upstairs because they usually come with strollers which couldn't get up the winding staircase, snuggled in chatting with his mother.

So I went and sat on the right side in the front and eavesdropped.

Little boy: Where is Anton?

Mother: Oh, he's long since at nursery school. We're very late.

Mother: Look, they've filled in most of the potholes. [We're driving past a longterm pipelaying project that's been going on since we arrived last August and will go on past our departure this August.] Now you can walk along here without falling into holes. Oh, there's a hole that's still pretty big.

Little boy: What if a little kid runs into the street? 

Mother: Well, the bus driver watches out and he'll stop. And the other drivers also watch out.

[Pause]

Little boy: So, I could run out into the street too!

Mother [in a certain amount of alarm, but still speaking pretty calmly]: Oh, no, you don't want to do that. The bus driver might not see you after all.

Little boy: But you said they watch out!

Mother: Well, they try, but you never know if they'll see you. There are always cases, it happens periodically, that kids run out into the street . . . 

[I had to leave the bus around this time. My transcript above isn't perfect because it's layered with trying to remember it since yesterday about this time, and also translating it from German. But that was generally it. I wanted to tell the boy, and his mother: yes, your logic is perfect little boy, of course it makes sense that if all the drivers are watching out then little children can safely and happily run anywhere they want including into the street, but what you are both groping for here is the concept of redundancy, which we absolutely need because systems fail. We teach our kids not to run into the street because drivers may not watch out perfectly; we teach our drivers to watch out because children might not always be able to keep from running into the street; we lock the door in a shared bathroom so as not to get walked in on in case someone forgets to knock and we also knock before walking in in case someone forgot to lock the door; and mostly, we always try to take the position of watching out in case someone else did their part of forgetting. (Sorry, the bathroom analogy is what sprang to my mind yesterday in the bus; I said nothing but I really wanted the mother to make the redundancy point to her fantastically logical tiny boy, because otherwise it seemed so clear he was going to go on being brilliant about how right it was for himself to run into the street.)]