The idea that we are finished, once we have sorted out our beliefs and that we never have to examine them again is a very limiting idea. The truth is that the beliefs we grew up with may not serve us very well at all when we are grown. They might, but then again they might not and it is our responsibility to ourselves to figure that part out.
Once upon a time, when we were just starting out learning new ideas, we had no old beliefs to change. Whatever we accepted into our hearts was true, we had no filters in place to keep ideas away from our hearts. As we walked along a bit farther on the path of our lives, we did put those filters into place, but they only served to protect the beliefs we already had.
Even though our old beliefs had value, they worked for us, brought us comfort and made our journey understandable, sometimes it simply get to the point where we need to replace them, because they just don't cut it anymore. Then it is time to let them go and get ourselves some shiny new beliefs that work for us in the present moment.