Murphy's Laws of Tools:
The next tool you need is the one that you left in the basement.
Box end wrenches- a tool designed to skin knuckles.
You have every size of bolt or screw you can imagine, except the one you need.
Your cordless drill will always need to be charged just when you need it.
If you really really need a specific tool- you can't find it.
Your grease gun will always be empty or air locked after two shots.
No matter how many socket extensions or adapters you have there will be a bolt in the project that you can't get a socket on.
General rules for auto or bike repair:
The Japanese have smaller hands than we do.
You can't buy the part- you have to buy the assembly.
The car that you've slowly been picking clean at the wreckers has been scrapped.
For back yard mechanics:
No matter how good the weather forecast it will always start raining after you've got it all apart.
Something you've been putting off will always fail completely on the coldest day of the year.
Hand held drilling is never straight.