Here is a rule whose very statement proves the rule to be false. The rule is
Every rule has an Exception
So going by its statement, even this rule should have an exception, which means not every rule has an exception, because there is at least one rule which has no exception, which in turn means the statement of the rule is false! So guess it would be more appropriate to rephrase it to say something like “Every rule has an Exception, except for this rule”.
If it is not clear, let me rephrase the logic.
The rule says that “Every Rule has an exception”.
Now this in itself being a rule, even this rule should have at least one exception. Isn’t it?
So, if this rule has an exception, then it cannot be “Every” rule, because there is one rule, which is the exception, which is outside the boundaries of this “Every”.
Which in turn means, not all rules have an exception, and so the use of the term “Every” becomes inappropriate.
So without validating any other rule for an exception, if the statement should still sound correct, then we should probably rephrase the rule as
Every Rule has an Exception, except for this rule.
Now if that was about logic, when we come to real life cases, finding even a single rule which has no exception will make this rule invalid.
For instance, there can be no exceptions to rules like “Gravity always attracts” !