Most of what happens in the technical world follows a standard pattern of behaviour. People wake at their usual time, machines are turned on as a fixed time and share prices following a similar pattern of change. Each of these events generates a series of data that can be monitored and used for evaluation purposes.
You wake in a morning, make a hot drink and this generates a spike in electricity usage from the kettle. Your computer is turned on when you arrive in the office, again, creating a rise in electricity usage and a production line runs at a fixed speed, generates a fixed level of heat from the motors and uses a predefined amount of electricity.
However, when these patterns of behaviour change the pattern within the recorded data also changes.