Simultaneous Attack and Defence

I was involved in a discussion on this on another site and thought that I would post this here as well, "Simultaneous Attack and Defence" is one of the underlying attributes of Wing Chun, does it mean that we Strike and Defend at the same time? No it does not, sometimes it will be the case but most likely not, sometimes we will Strike before we Defend, what we do is begin the Process of "Simultaneous Attack and Defence" at the same time, what lands first will be determined more by the position and action of the opponent than by our design.