The seven guiding principles in ITIL 4 are important because on the exam there are two exam objectives that are going to cover these seven guiding principles. The first is to describe the nature, use, and interaction of these seven guiding principles while the second objective is to explain the use of these seven different guiding principles. It's not important to memorize these guiding principles necessarily but you're actually going to have to explain and describe, which is a higher level of effort inside the exam.
So, what is a guiding principle? A guiding principle is a recommendation that's going to guide an organization in all circumstances. They can be used to guide an organization in their work as they adopt a service management approach and adapt ITIL guidance to their own specific needs and circumstances. This means that all organizations are going to integrate the use of multiple different methods into their overall approach to service management. The way you do service management and the way other organizations do service management might be different. But both organizations should be based on the same guiding principles because these guiding principles are applied universally to every initiative out there. These guiding principles are going to help us to encourage and support organizations in their continual improvement across all levels of the organization. These are applied universally to all of the initiatives and all of the relationships with your organization's different stakeholder groups. So, the consumers and the customers and the stakeholders across the organization, all of these people need to be considered when you're thinking about these guiding principles.
As an organization, you're not going to use just one or two of these principles. You should consider all seven of them, and determine which ones are relevant for each situation and how you should apply them. Not all of the principles are going to be critical in every situation. But you're probably going to find that five or six, or even seven of them, may apply to your organization's initiative. Think through each of them like a check list to make sure you're thinking about your service in a holistic way. As you do this and you review each of them, you will have a way to determine whether or not they're appropriate for your service and decide if it should be applied.