Debugging is twice as hard as writing the code in the first place.
Therefore, if you write the code as cleverly as possible, you are, by definition, not smart enough to debug it.

~ Kernighan, Brian W., and P.J. Plauger. The Elements of Programming Style. 2nd. ed. New York: McGraw-Hill Book, 1978. Print.

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.

~ Knuth, Donald E. The Art of Computer Programming. 2.nd ed. Reading (MA): Addison-Wesley, 1980. Print. Addison-Wesley Ser. in Computer Science and Information Processing.

~~ (TBA)

As software developers we get to learn many good practices and strive to apply them in our code.

For instance we learn the importance of good naming of variables and functions, encapsulation, class cohesion, the usage of polymorphism, conciseness, readability, code clarity and expressiveness, and many others.

What if there was only one principle to know instead of plenty of best practices ?

I believe this principle exists: it consists of Respecting levels of abstraction.

This is the one principle to rule them all, because applying it automatically applies all the above best practices, and even more of them. When you follow it, your code writes itself out well naturally.

~ Boccara, Jonathan. It all comes down to respecting levels of abstraction. Fluent C++, 2016-12-15. https://www.fluentcpp.com/2016/12/15/respect-levels-of-abstraction/