An exception to the rule that all rules must have exceptions would imply that the original premise (in your question) cannot be true.
There are two lessons to be learnt here.
The first is that we (aspiring writers) need to be very careful: semantically, when using words that infer an absolute state - words like, 'all' or 'every' - we need to be sure that sentences containing these words do so logically.
The second thing to take away from this is - if you are going to make an exception to a rule then don't get caught. If you can manage this - without exception - then you should live long and prosper.