Even if metrics are the most used tools for assessment and management, they are often misused. The classic quote about the importance of measuring comes from Tom deMarco:

You cannot control what you cannot measure.
Tom deMarco

This quote is often used as a means to urge people to use metrics. The common translation is that a good manager has to use metrics to control the state of affairs. As a consequence measures are more or less willingly imposed into the development process. Which metrics? Unfortunately, any metrics. The more, the better.

However, if we take a closer look at the quote, it is not actually about the use of measures. It is about the ability to measure. The quote says that you cannot say you are in control if you are not able to quantify the state of affairs. In other words, you have to be able to quantify what is important.

Why? Lord Kelvin explains:

When you can measure what you are speaking about and express it in numbers, you know something about it; but when you cannot measure it, when you cannot express it in numbers, your knowledge is of a meagre and unsatisfactory kind: it may be the beginnings of knowledge but you have scarcely in your thoughts advanced to the stage of Science.
Lord Kelvin

Before starting to measure, we first have to think about the essence of our subject. At the beginning, this essence is not concrete, and it is typically not measurable. This is an unwanted situation. Galilei goes a step further and calls for action:

What is not measurable, make measurable.
Galileo Galilei

Galileo urges us to reshape our approach to what we are doing in a way that allows us to measure it. He tells us to make it explicit.

We can find many ways to measure a certain situation, but in the end, it is the act of making things explicit that places us in a position to make better decisions. And ultimately, it is decision making we should focus on.