Most businesses have some form of vulnerability scanning running. It produces a list. The list is long, mostly informational, and nobody has time to read it.
That list has a specific blind spot: it evaluates findings one at a time. A scanner does not know that the shared password on a printer is also the password on a file server, or that a legacy protocol nobody remembers enabling is quietly handing out credentials to anything that asks.
An attacker does not work through a list. They chain findings together — a weak credential here, a cleartext protocol there — until the chain reaches something worth stealing. Individually, each link looks like a medium. Together they're a domain compromise.
Penetration testing is what closes that gap. Instead of listing what's exposed, we attempt the attack and document how far it gets.