Riddle: The cost of making only the maker knows, valueless if bought, but sometimes traded. A poor man may give one as easily as a king. When one is broken pain and deceit are assured. What is it?
When you think about it a little bit, it seems impossible that there could be something that a poor man may give as easily as a king.
However, according to the riddle, it is not impossible. Also, this thing sounds very valuable since it would cause pain and deceit when it is broken. I bet thus far you thought that it was something material, but it is not. With this in mind, you may figure out that the answer is a promise. A promise’s cost is only known to its maker, it cannot be bought, yet it can be traded.
The answer is: Promise.