Donald Knuth

"Beware of bugs in the above code; I have only proved it correct, not tried it."

"I can’t be as confident about computer science as I can about biology. Biology easily has 500 years of exciting problems to work on. It’s at that level."

"The psychological profiling [of a programmer] is mostly the ability to shift levels of abstraction, from low level to high level. To see something in the small and to see something in the large."

"The important thing, once you have enough to eat and a nice house, is what you can do for others, what you can contribute to the enterprise as a whole."

"The whole thing that makes a mathematician’s life worthwhile is that he gets the grudging admiration of three or four colleagues."

"Science is what we understand well enough to explain to a computer. Art is everything else we do."

"A mathematical formula should never be "owned" by anybody! Mathematics belong to God."

"I define UNIX as 30 definitions of regular expressions living under one roof."

"I can’t go to a restaurant and order food because I keep looking at the fonts on the menu."

"I have been a happy man ever since January 1, 1990, when I no longer had an email address. I'd used email since about 1975, and it seems to me that 15 years of email is plenty for one lifetime."

"Email is a wonderful thing for people whose role in life is to be on top of things. But not for me; my role is to be on the bottom of things. What I do takes long hours of studying and uninterruptible concentration."

"How can you own [...] numbers? Numbers belong to the world."

"In fact, my main conclusion after spending ten years of my life working on the TEX project is that software is hard. It’s harder than anything else I’ve ever had to do."

"If you find that you're spending almost all your time on theory, start turning some attention to practical things; it will improve your theories. If you find that you're spending almost all your time on practice, start turning some attention to theoretical things; it will improve your practice."

"In a way, you'd say my life is a convex combination of English and mathematics. ... And not only that, I want my kids to be that way: use left brain, right brain at the same time – you got a lot more done. That was part of the bargain."

"A good technical writer, trying not to be obvious about it, but says everything twice: formally and informally. Or maybe three times."

"I am assuming that God exists and I am glad that there is no way to prove this. [Because] I would run through the proof once, and then I'd forget it, and I would never speculate about spiritual things and mysteries otherwise. And, I think, my life would be very incomplete."

"I came to philosophy finally phrased as "0.8 is enough". … If I had a way to rate happiness, I think it's a good design to have an organism that's happy about 80% of the time. If it was 100% of the time, it would be like everybody's on drugs and everything collapses and nothing works because everybody is just too happy. … There are times when I am down and I know that I've actually been programmed to be depressed a certain amount of time."

"Let's face it, if there were 10 people like me in the world, we wouldn't have time to read each other's books."

"Most people only know pi in decimal."

"By understanding a machine-oriented language, the programmer will tend to use a much more efficient method; it is much closer to reality."

"An algorithm must be seen to be believed."

"People who are more than casually interested in computers should have at least some idea of what the underlying hardware is like. Otherwise the programs they write will be pretty weird."

"Random numbers should not be generated with a method chosen at random"

"The sun comes up just about as often as it goes down, in the long run, but this doesn't make its motion random."

"The reason is not to glorify "bit chasing"; a more fundamental issue is at stake here: Numerical subroutines should deliver results that satisfy simple, useful mathematical laws whenever possible. [...] Without any underlying symmetry properties, the job of proving interesting results becomes extremely unpleasant. The enjoyment of one's tools is an essential ingredient of successful work."

"Any inaccuracies in this index may be explained by the fact that it has been sorted with the help of a computer."

"Trees sprout up just about everywhere in computer science..."

"Science is knowledge which we understand so well that we can teach it to a computer; and if we don't fully understand something, it is an art to deal with it."

"In this sense, we should continually be striving to transform every art into a science: in the process, we advance the art."

"The real problem is that programmers have spent far too much time worrying about efficiency in the wrong places and at the wrong times; premature optimization is the root of all evil (or at least most of it) in programming."

"To summarize: We have seen that computer programming is an art, because it applies accumulated knowledge to the world, because it requires skill and ingenuity, and especially because it produces objects of beauty. A programmer who subconsciously views himself as an artist will enjoy what he does and will do it better. Therefore we can be glad that people who lecture at computer conferences speak of the state of the Art."

"Let us change our traditional attitude to the construction of programs: Instead of imagining that our main task is to instruct a computer what to do, let us concentrate rather on explaining to human beings what we want a computer to do."

"For his major contributions to the analysis of algorithms and the design of programming languages, and in particular for his contributions to the "art of computer programming" through his well-known books in a continuous series by this title."