Despite open source is developed by a bunch of hackers who keep delivering buggy code, you can still close your eyes and install Ubuntu and it will usually work in 95% of cases.
Even if you go to the most popular fast food outlet during the busiest of hours, you usually get to eat that tasty pizza even the humans did not all procedures. You see, they are humans, they may err but they have an uncanny judgment that comes from practice which is capable of finding and fixing their errors before they are delivered.
We have millions of explosive-powered heavy metal boxes running fast on unprotected lanes, their path solely directed by unreliable biological organismes following conventions from blinking lights and painted signs.
But most of the time, it works.
A handful of singular individuals penned the broad outlines of our Constitutional structure, but it's the masses of people that built the system and keep it running. The difference between say Bangladesh and the United States is not the ingenuity of their respective founding documents, but the file clerk at the American courthouse who wouldn't even think of taking a bribe, versus his counterpart.
Big ideas mean nothing without execution, and it's the plebes that do the execution. Every great endeavor lives and dies by the virtue of the rank-and-file people undertaking it.
I'm guessing humans have evolved to "work" even when our uniquely intelligent brains combine with our opposable thumbs to fuck things up.
Any intelligent species can make a mistake, but it takes a human to really fuck things up.