If there's a possibility of several things going wrong, the one that will cause the most damage is the one that will happen.
If anything just can't go wrong, it will anyway.
If everything seems to be going well, you've overlooked something.
Those who know the least know it the loudest.
Smile...tomorrow will be much worse.
Nothing is as easy as it looks.
Everything takes longer than you think.
If you want something bad enough, chances are you won't get it.
When you set out to do something, something else must be done first.
The other line always moves faster.
Whatever hits the fan will not be evenly distributed.
Don't mess with Mrs. Murphy.