Many operating systems touted as more ‘modern’ or ‘user friendly’ than Unix achieve their surface glossiness by locking users and developers into one interface policy, and offer an application-programming interface that for all its elaborateness is rather narrow and rigid. On such systems, tasks the designers have anticipated are very easy — but tasks they have not anticipated are often impossible or at best extremelypainful.

Unix, on the other hand, has flexibility in depth. The many ways Unix provides to glue together programs mean that components of its basic toolkit can be combined to produce useful effects that the designers of the individual toolkit parts never anticipated.

Unix's support of multiple styles of program interface (often seen as a weakness because it increases the perceived complexity of the system to end users) also contributes to flexibility; no program that wants to be a simple piece of data plumbing is forced to carry the complexity overhead of an elaborate GUI.

Unix tradition lays heavy emphasis on keeping programming interfaces relatively small, clean, and orthogonal — another trait that produces flexibility in depth. Throughout a Unix system, easy things are easy and hard things are at least possible.