1. Subjectively, experientially, phenomenologically, you are always where you are. Your body might move from A to B, but you – your sense of self – do not move. You are remaining in one and the same place of experiential am-ness. You are a space that is aware, a field of awareness, a coordinate of existence that is independent of its physical coordinates. That is the First Face of subject permanence.
2. The second face of subject permanence is the habit of seeing the First Face (the Original Face). You know, how as kids we develop object permanence: just because the ball is out of sight it doesn’t mean that it does not exist. This is known as object permanence (knowing that an object has constancy). Subject permanence is a habit of seeing who you are behind the veil of who you are not. You might introduce yourself to someone by saying: “Hi, I am so-and-so’s so-and-so,” and just as you are saying this deep inside you know that you are not so-and-so’s so-and-so. Subject permanence is knowing that you-as-the-subject exist even when you lost sight of yourself, knowing that you are your own so-and-so, knowing that you are not even a so-and-so, knowing that you are not any Form or any Circumstance, knowing that you just are. Subject permanence – in its ultimate form – is never losing sight of your original (first) face.
Meditate on this if this is not clear. True clarity of what this means, in my opinion, can only be gleaned through meditation.