One question raised upon watching or reading MacBeth is "how responsible are the witches"" The argument for the witches responsibility is that without them intervening then MacBeth would never had killed Duncan, as he never would have thought of it. The argument against them being responsible is that they simply told MacBeth what he was going to do, and he was going to do it anyway, irrespective of their intervention. If he were going to do it anyway then why would they tell him"

If fate were to carry itself out even without their participation then there would be no purpose to them warning MacBeth. Through this logic you can ascertain that the witches were directly intervening with fate in order to bring upon King Duncan's death. Otherwise all their actions would be superfluous. This is not the larger picture though; this is not fate in relevance...