The three basic ingredients of any business are technology, processes and people. From an IT security standpoint, which of these is the weakest link in your organization? Whichever it is, it is likely to be the focus of attack.
Organizations around the globe routinely employ the use of powerful firewalls, anti-virus software and sophisticated intrusion-detection systems to guard precious information assets. Year in and year out, polls show the weakest link to be processes and the people behind them. In the SIEM world, the absence of a process to examine exception reports to detect non-obvious problems is one manifestation of process weakness.
The reality is that not all threats are obvious and detected/blocked by automation. You must apply the human element appropriately.
Another is to audit user activity especially privileged user activity. It must match approved requests and pass the reasonableness test (eg performed during business hours).
Earlier this decade, the focus of security was the perimeter and the internal network. Technologies such as firewalls and network based intrusion detection were all the rage. While these are necessary, vital even, defense in depth dictates that you look carefully at hosts and user activity.