I have been thinking lately that the longer I am in this business, the more I am amazed that any software anywhere runs successfully at all.  Every scenario has to be accounted for.  Every detail has to be precise.  There are so many opportunities for error, from translating requirements, to miscommunications, to un-anticipated inputs, to simply flaws in logic and typos.  Not to mention the equally complex task of maintaining the necessary system, storage, and networking environment for the program to run within.

In Code Complete, Steve McConnell talks about this foolhardy profession.

Nobody is really smart enough to program computers.  Fully understanding an average program requires an almost limitless capacity to absorb details and an equal capacity to comprehend them all at the same time. The way you focus your intelligence is more important than how much intelligence you have.

At the 1972 Turing Award lecture, Edsger Dijkstra delivered a paper titled "The Humble Programmer." He argued that most of programming is an attempt to compensate for the strictly limited size of our skulls. The people who are best at programming are the people who realize how small their brains are. They are humble. The people who are the worst at programming are the people who refuse to accept the fact that their brains aren’t equal to the task.

The purpose of many good programming practices is to reduce the load on your gray cells. You might think that the high road would be to develop better mental abilities so you wouldn’t need these programming crutches. You might think that a programmer who uses mental crutches is taking the low road. Empirically, however, it’s been shown that humble programmers who compensate for their fallibilities write code that’s easier for themselves and others to understand and that has fewer errors.

Speaking of Dijkstra, he knew this already in 1968.  In "The Structure of the T-H-E Multiprogramming System," wherein he describes the design of one of the first multitasking systems, he gives props to his students:

"The other remark is that the members of the group have previously enjoyed as good students a university training of five to eight years and are of Master’s or Ph.D. level. I mention this explicitly because at least in my country the intellectual level needed for system design is in general grossly underestimated. I am convinced more than ever that this type of work is very difficult, and that every effort to do it with other than the best people is doomed to either failure or moderate success at enormous expense."