Cromwell’s rule, named by statistician Dennis Lindley, states that the use of prior probabilities of 1 (“the event will definitely occur”) or 0 (“the event will definitely not occur”) should be avoided, except when applied to statements that are logically true or false, such as 2+2 equaling 4 or 5.
If a belief is 100% true then it is a fact.
According to Cromwell’s rule, you should always have at least a little bit of doubt in your beliefs. Meaning you should always hold the possibility that your belief may be wrong. This means that your belief is only a guess as to what is real.
The fact that we do not actually see the real world, that we only have what our brain interprets through our senses adds credence to that idea. What your brain interprets of what is out there and what is really there could be two very different things.
Scientific theories are a type of belief. Any theory could be proved wrong, but a theory can never be proved correct. The best theories are those theories that best predict a future event. For the longest time, Newton’s theories accurately proved the future. When the theory was applied at the subatomic level it was no longer accurate. New theories that included the subatomic level replace Newton’s theory. As a simpler theory, Newton’s theory works well in predicting things in the macro world.
For beliefs, we need to take a similar approach. For any given belief we need to ask the question, does it serve me, and does it serve the world. If the answer to these two questions is yes it is a good belief to have.
Too often we become attached to our beliefs and we stop evaluating our beliefs and we just hold them as facts. Eventually, one of our beliefs will not serve us and put us in an unwanted position.