In our Sunday evening fellowship study of Jacob's story in Genesis, we talked about the failures we all have and have had since the beginning of civilization. Given the redundancy of mistakes generation after generation, you could conclude that little progress has been made when viewed as a community even as individuals improve independently of each other.
The statistician in me kicked in. Since we are not (and will never be) perfect you could use the analogy of the machine uptime or quality control dependencies. Take four independent operations (probably not the best assumption with people but it will do) that each have different failure rates - 1%; 3%; 5%; and 0.1%. The probability that the "integrated system" fails is 8.86%.
The more independent functions you have will create a multiplier effect in the resulting failure rate. If you had ten operations all with 99.9% quality output (sounds pretty close to perfect) you should expect a 1% defect rate overall.
So since we all fall short of perfect - when you put an entire population into the equation - you get a pretty big failure rate. But as Thomas Edison would say - we have found 1000 ways that can cause failure - but that doesn't mean we've failed 1000 times.