Quiet sitting does not always mean that you are really meditating. This is especially true for Zen meditation, and if you decide to seriously engage in Zen practice, you should be prepared to accept that learning to “just sit” is not as easy as it sounds. At the same time, it will require more and less of that what you have done before.
That's why it is important to learn the correct technique right from the start: how to properly sit, breath and let go of mental processes. Failure to do so will not provide a solid foundation, and the practitioner will be constantly dominated by the old mental patterns and neural responses that eventually limit further progress.