A few weeks ago an IT admin at a university discovered a piece of Mac malware that, until then, no-one was aware of. As it was likely part of a targeted attack, not a single antivirus solution knew of it so no protection was offered against it. The malware was discovered because the network security team at that university spotted unusual network behavior originating from a single machine. This prompted the IT admin to investigate and lead to the malware being uncovered. Then the malware sample was distributed in the security community where security researchers and antivirus vendors pulled it apart, analyzed it and started offering protection against it.
The network security team probably could not have uncovered the malware and the IT admin probably couldn’t have analyzed the network traffic to spot the anomalous behavior. And neither the security team or the IT admin could have analyzed the malware sample in a way a professional malware researcher does. Each person or team involved in the above story has their own expertise and they all make up different layers of a security solution.
Layered security is recommended for a reason, the chances of protecting you from *name a risk here* increase as layers of protection are added. You can harden your macOS installation by tweaking certain settings and you can install security software to do all the things macOS can’t do. I wrote a little about security in layers and which software can help you become more secure here.