The guiding force of the universe has a great sense humor. It loves to have some fun at our expense. You wait in a long queue and when your turn comes the counter is closed for lunch. It usually rains on the days you forget to carry the umbrella. There seems to be some uncodified principles governing the frustrated lives of us mortals. Man in his endeavour to know the why and how of everything has attempted to decipher those operating principles.
Excerpts from Arthur Bloch's Murphy's Law - and Other Reasons Why Things Go Wrong:
The Unspeakable Law
As soon as you mention something,
If it's good, it goes away.
If it's bad, it happens.
Nonreciprocal Law of Expectations
Negative Expectations yield negative results.
Positive expectations yield negative results.
Every man has a scheme that will not work
Zymurgy's First Law of Evolving Systems Dynamics
Once you open a can of worms, the only way to recan them is to use a larger can.
The other line moves faster.
Law of Selective Gravity
An object will fall so as to do the most damage.
A man with one watch knows what time it is. A man with two watches is never sure.
and of course...
If anything can go wrong, it will.