You should take Murphy's law into consideration whenever you are preparing for an important speech. For example, if you are preparing to make a power point presentation, ask yourself these questions - What would I do if the projector fails to recognize my computer? What if the power goes off during my speech? What if my computer crashes? What if my computer doesn't connect to the network to access the presentation material?
It is hard to beat Murphy ! But, it is absolutely possible to minimize Murphy's impact on our speeches/presentations. Experienced speakers learn to identify all the dependencies in advance. They'll have sufficient back up plans, in case there are technical issues. Simple things like going to the speech venue in advance, verifying the functioning of the props before the speech, carrying a USB stick with power point slides (instead of relying on a network storage), having a backup laptop, having handwritten charts etc., would help ease many anxieties caused by technical glitches.