Causation - Hume

I think that Hume raises an strong point when he is talking about our knowledge on matters of fact, that they are tied to cause and effect. Just because an event has happened given a certain cause in the past doesn't mean that it needs to happened that way again or is necessary for the event to occur. Of course, logically it would certainly be a shock if something that has caused a given effect occurred without any difference for some extended stretch, would suddenly change, but it is possible. Of course the next part of the question needs to be...so? Knowing that there might be an unexpected effect instead of the intented effect, does it change the effect or the reason to take a certain action. I certainly don't think so...