This practice is sometimes called shikantaza, or just sitting. "Just sitting" sounds simple, doesn't it? Yet, most of us sitting here with distraction, confusion, pain, don't experience our sitting as simple at all. To JUST do something - to do it wholeheartedly, totally present in the experience of doing it - has become something of a Zen cliche - one that has infiltrated the culture of NIKE ads - JUST do it - &¬ Nancy Reagan's anti-drug slogan - JUST say No. But even the athletes who are capable of JUST doing it on the field, don't seem to have an easy time of JUST saying no when it comes to drugs. Most of us are that way - able to stay focused and present in some aspects of our lives, but easily distracted and defensive in many other realms. So we practice by paying attention to our areas of resistance, the boundaries of our willingness to pay attention. Just sitting isn't passive, it includes this active, vigilant attention. And how we follow the zendo rules, how meticulous or careless we are with the details of zendo procedure, is one measure of how well we bring this attention off our cushion into our everyday life - which in the end is the whole point of our practice.
Just sitting is simple the way just living your life is simple. And when you are genuinely willing to simply face anything and everything comes up in your life, then you are entitled to say that "just sitting" is a simple practice.