because that that's just how we think about it and so the first thing the encoder does is it decodes Z from the bit stream so the encoder knows X so the encoder can compute Q of Z given X this is just the approximate posterior of this latent variable model and it can use this distribution to decode from the bit stream and we assume that this bit stream was full of random bits and so that this is a question that came up and I'll talk about the consequences of that later so that's the first thing you do but the point is that if you decode from