The traditional approach to security assumed that anything inside the network perimeter could be trusted. The firewall was the wall. If you were inside it, the system assumed you belonged there.
That model made sense when everyone worked from a fixed office, on company hardware, connected to a single network. It no longer reflects reality. Today, users access business systems from home, from mobile devices, from cloud applications, and from locations the organisation does not control. The perimeter does not exist in any meaningful sense, and relying on it as a primary security control is a structural vulnerability.
Zero Trust replaces that assumption with a different one: trust nothing by default. Every access request regardless of whether it comes from a known user, a managed device, inside the office, or from the cloud, is treated as potentially hostile until it is verified. Verification is continuous, not one-time. Access is granted based on identity, device health, context, and the principle of least privilege which is the minimum access needed to complete the task, and nothing more.
You cannot go to a security vendor and buy Zero Trust. Zero Trust is a methodology. It's a set of principles that shape how your entire security environment is designed and operated. The technology supports the principles. The principles come first.