At the end of the day, a heuretic is “complete” when it can survive outside of the head of the person who created it. In this way, brains are wombs for heuretics. A heuretic isn’t ‘viable’ until it can exist separate from the mind it came from. This is another way in which heuretic evolution is similar to biological evolution.
There’s something about a heuretic not being viable unless it can be tested against something.