I have the privilege of being born a Murphy. When you are born a Murphy, you become accustomed to being called Murph or Murphy you’re entire life. This includes your childhood. I think most of my friends do not realize I have a first name.
It probably comes from television and movies. If there are police in a film, at least one of them is a Murphy. He might not be the main character, but there is always at least one Murphy on the squad.
Another thing, you always get blamed if something goes wrong. Especially if you are not present.
I currently work in IT for a large multi-national company. Since I am always looking for things that can go wrong, when people listen to me, things go right. I can not count the times I told a project manager something was going to go wrong if they continued down a certain path. In all the time I have worked with project managers, I have yet to be wrong.
So, if somebody named Murphy advises you not to go down a certain path, you might want to listen. We have been seeing things go wrong all of our lives.