A posterior $p(\theta\vert x) = \frac{p(x \vert \theta)p(\theta)}{p(x)} $
Many materials say that since the $p(x)$ is a constant, the $p(x)$ can be ignored. Thus, $p(\theta\vert x) \propto p(x \vert \theta)p(\theta)$
My question is why $p(x)$ is a constant and ignored. Is this because even though we don't know the distribution x, there is a corresponding true distribution for $x$? So, $p(x) $ is a constant (we don't know but already determined) and thus, can be ignored?