Murpheys law...

I always had the impresion that any "Murpheys law" is self
propogating. Take Mr. Murpheys 1st law, something about "if a
system can be put together wrongly, it will" - but I bet he focused on
the 1 bad connection, not the 1000 correct ones.
What I'm trying to say (badly) is that once we start to fixate on
something, expecting it to go wrong, then we'll notice every time it
does go wrong and remember it, but won't notice when the opposite
happens.
eg. I have a thing against French drivers - if I see French number
plate on a car I'll watch them to see what they do wrong. When they
do something worng, I'll think "yes, another bad French driver". Now, if
they had a different number plate I wouldn't have been watching them
so wouldn't have seen the mistake that any driver of any nationality
could have made (such as signalling off roundabouts, which NOONE
does here).
Hope that long drivel makes some sense - if not, I blame it on the
nicotien withdrawel.

Your prejudice against French drivers probably has some element of truth in it.

On the other hand, Murphy's law is one of several beliefs that emerge as a result of the way
we think. They emerge spontaneously, and are very difficult to shake off, even if you know
them to be false. For example, my parents both have PhDs in scientific subjects, and my dad
particularly is fairly anti-religion, and yet they talk about "commentator's curse" when
watching sport, say continually that England are playing badly and are about to lose, no
matter how well they are doing, and think that rain is caused by leaving washing out to dry!

The same phenomenon explains why some people have relatively little fear of driving, but an
immense fear of GM food, even when the former carries a significant risk of death or injury
and is definitely unhealthy in terms of the exhaust fumes you're breathing in and the lack of
exercise involved, while the latter might possibly be 'bad for you' in an ill-defined way,
simply because it's 'unnatural', as if any kind of agriculture is 'natural'. Death is scary, but
the unknown is even scarier.