Up to this point, we used some of the built-in actions and filters, while explaining the practical uses. However, you might be still trying to grab the concept, as it's not a practice used in pure PHP development. The process gets even tougher when coping with the lack of knowledge in the action execution process.
What is the action execution process?
WordPress has a set of built-in actions that are executed within the loading process of each and every request. Each of these actions has a sepcific responsibility in the loading process. The actions used for the loading process are executed in a predefined sequence. However, The WordPress Codex specially mentions that we shouldn't rely entirely on the loading process as it can vary based on the other components in the site.