A good worker must know how to use his or her tools effectively. Amazingly, most people don't know what their best tool is.

What is mankind's most important tool?

Here are five hints:
1. It is a very old tool, but we are still improving it.
2. It is not shelter or clothing. We use it to make shelter and clothing. It is not the brain or the hand. It was created by humans.
3. It was developed by people world-wide; and there are about six thousand named varieties.
4. It is our greatest tool by far. Over the centuries, it's use has enabled us to build allmost everything from buildings to computers.
5. You use at least one most of the time. Sometimes people even use one in their sleep!