It comes to no surprise, that any microservices, any security controls you use to build applications – will eventually be broken (or fail). Under certain pressure, some components will fail together.
The question is – how do you build your systems in a way that security incidents won't happen even if some components fail. And the data leaks won't occur even if penetration tests are successful.
"Defense in depth" is a security engineering pattern, that suggests building an independent set of security controls aimed at mitigating more risks even if the attacker crosses the outer perimeter.