Because "Security is a journey, not a destination".

There's always a way to enhance your processes, monitor more indicators, etc. or otherwise improve your security.

Sometimes you don't know what to monitor until you know the attack vector. We are only human

1. Because humans aren’t perfect. 2. Because mistakes happen. 3. Because there’s a cost to everything: if you want better security, it’s going to cost you more, immediately. And we don’t always estimate trade-offs correctly (see points 1 and 2).

Exactly.. life in general is about constant refinement.. if today's hacker could time travel to 1999, she would be in a nirvana of Bind, SSHv1, Apache, IIS etc.. vulnerabilities. Hacks happen and we learn and improve, even down to the language being used.. a la Rust.