Programmers have a strong tendency to underrate the importance of good style. Eternally optimistic, we all like to think that once we throw a piece of code together, however haphazardly, it will work properly the first time and ever after. Why waste time cleaning up something that is almost certain to be correct? Besides, it probably will be used for only a few weeks.The above text is part of the Epilogue of The Elements of Programming Style
There are really two answers to the question. The first is suggested by the word "almost". A slap-dash piece of code that falls short of perfection can be a difficult creature to deal with. The self-discipline of writing it cleanly the first time increases your chances of getting it right and eased the task of fixing it if it is not. The programmer who leaps to the coding pad or the terminal and throws a first draft at the machine spends far more time redoing and debugging than does his or her more careful colleague.
The second point is that phrase "only a few weeks". Certainly we write code differently depending on the ultimate use we expect to make of it. But computer centres are full of programs that were written for a short-term use, then were pressed into years of service. Not only pressed, but sometimes hammered and twisted. It is often simpler to modify existing code, no matter how badly written, than to reinvent the wheel yet again for a new application. Big programs — operating systems, computers, major applications — are never written to be used once and discarded. They change and evolve. Most professional programmers spend much of their time changing their own and other people's code. We will say it once more — clean code is easier to maintain.
One excuse for writing an unintelligible program is that it is a private matter. Only the original programmer will ever look at it, and surely he need not spell out everything when he has it all in his head. This can be a strong argument, particularly if you don't program professionally. But even if only you personally want to understand the message, if it is to be readable a year from now you must write a complete sentence.
You learn to write as if to someone else because next year you will be "someone else". Schools teach English composition, not how to write grocery lists. The latter is easy once the former is mastered. Yet when it comes to computer programming, many programmers seem to think that a mastery of "grocery list" writing is adequate preparation for composing large programs. This is not so.
The essence of what we are trying to convey is summed up in the elusive word "style". It is not a list of rules so much as an approach and an attitude. "Good programmers" are those who already have learnt a set of rules that ensures good style; many of them will read this book and see no reason to change. If you are still learning to be a "good programmer", however, then perhaps some of what we consider good style will have rubbed off in the reading.
— The Elements of Programming Style (Second Edition)
by Kernighan and Plaugher
by Kernighan and Plaugher.
See also: Elements of Programming Style fortune mod.