A better saying is that zero days are... fragile? You use zero, someone notice, it gets fixed. And yes, they are rare compared to the vast # of known vulns.

A better saying is that zero days are... fragile? You use zero, someone notice, it gets fixed. And yes, they are rare compared to the vast # of known vulns. Ideally if given the choice, you'd utilize a known vuln against outdated software rather than risk burning your zero day.