Here's why:
* Precept means a rule of conduct or a general principle. It often refers to a belief or idea that is not necessarily proven but is accepted as a guiding principle.
* Unproven belief implies a concept that is not supported by evidence but is still held to be true.
While "precept" doesn't always imply a lack of evidence, it often refers to a belief held without rigorous scientific proof, making it a suitable synonym for "unproven belief."