Laziness

Gorden Bell:

The cheapest, fastest, and most reliable components of a computer system are those that aren't there.

Jon Bentley:

Those missing components are also the most accurate (they never make mistakes), the most secure (they can't be broken into), and the easiest to design, document, test and maintain

This has a parallel in data structures:

The fastest, most parsimonious, and best performing data structure is one which is never concretized. A promise to create data when--or if--it is needed is often easy to make.

Antoine de Saint Exupery:

A designer knows he has arrived at perfection not when there is no longer anything to add, but when there is no longer anything to take away.

Things to avoid doing (at this particular moment):

Expensive computation

Concretize large data sets

Time consuming backgroud operations