"Anything that can go wrong, will"
I.E. if you are in the car driving to work, and you know that u are running late, you will hit all the red lights and get all the traffic.
Trust me, it happens to me all the time =]
If you go on a picnic, it will rain.
If you go to the zoo, an elephant will sit on you.
If you drive to the gas station, you will run out of gas before you get there.