In a car engine the piston cannot do the crankshaft job. The crankshaft cannot do the connecting rod job. A spark plug just do one thing and the same can be said about the rest of the parts.
Computer software is more flexible, even so the Unix base system has a similar policy (sometimes referred to as KISS, acronym for "Keep it simple, stupid"), a group of small programs where each one do just one thing and do it well. And gives you a way to combine those small programs to get more complex tasks done.
More than two decades ago, when I was studying violoncello at the music conservatory of my country, Argentina, I decided to give a try to a luthier course an old man was giving on Saturdays. In case you don't know it, a luthier is who makes musical instruments, especially the stringed ones you see in orchestras. Some people get surprised when are told that to make a violin top the luthier starts from a square solid block of wood and gets the concavity by carving with gouges. He has to get this concavity preserving the same thickness on the whole top, controlling with a thickness caliper while carving. This is a really hard craft task and yes, the cello top is made in the same way. I understood I had to decide between playing or constructing them since both trades would demand me full commitment so, not without regret, I abandoned this course after a month. From this experience I keep a short dialog I had with the professor before leaving the course, he told me he had lived in the United States for several years where he had a job in a piano factory with a wonderful wage. When I asked him the obvious, why he went back to Argentina to win less than the seventh part of the money he won in the US, he told me he got bored of cutting stupid piano keys the whole working day. He was just a piece in a factory assembly line.
Modern society is a machine. It makes individuals do one thing and do it well, like in the Unix example. All day, everyday and, with “luck”, during a whole life. Of course this is economically productive but what's good for machines is not necessary good for people. As time passes, individuals resemble more and more pistons or spark plugs, their ability to get adapted to different contexts, distinctive quality of alive organisms, is getting atrophied.