Quality Software Management
Vol 2. First-Order Measurement

is the title of an excellent book by Jerry Weinberg. As usual I'm going to quote from a few pages:
Software development is not primarily a manufacturing operation for we (ideally) never develop the same software twice. This uniqueness of product means that Deming's "statistical signal" - though necessary - is not sufficient for feedback control, because there often isn't enough repetition - enough stability - to generate meaningful statistics.
In software we are attempting to obtain value by achieving higher precision than human beings have ever attempted before.
The switch from cost observation to value observation is the strongest indication that an organization has made the transition from Pattern 2 (Routine) to Pattern 3 (Steering).
Under emotional pressure, people literally stop thinking.
A fact becomes a feeling as soon as you observe it.
The triad has special significance for observation, because it is the first grouping in which there is both interaction and observation of interaction.
The way I remember the difference between faults and failures is to think of earthquakes. Faults (in the ground) leads to failures (in bridges, buildings, and so forth).
One of the most sensitive measures of the cultural pattern of any organization is how quickly it finds and removes problems.
Any plan is just a plan - a series of guesses about how the future will work out.
Bureaucracy: people doing things whose purpose they don't understand.