Your patterns of thought, existing bodies of knowledge, beliefs, predispositions, etc. are the 'stuff of your mental universe'. We are always subject to the power of our mental inertia. The waves in our mental oceans can never be magically stilled, and are therefore always impacting our new beliefs, even when we become scrutinizing adults. It is simply impossible to 'wipe the slate clean' and start over. These effects remain with us throughout our entire lives. Even the beliefs that we later discard are difficult to completely negate, and leave their own residual effects.