--||-|--|-|-|-|-|---|-|-|-|-|-|||-|-||-|-|-|-||-||Mostly people would consider this to be fairly random sequence (with "-" and "|" having an equal chance of appearing). It is not. The "|" has a 75% chance of appearing. A truly random sequence might look like this:
|----|-|||-|||-||---||------|||--||-------|--||-|-One reason for our poor randomness skills is that we imagine that things should be uniform in their randomness. The first sequence looks more random because the two symbols alternate more frequently. Gamblers often experience this problem: a run has held steady so they bet that a contrary pattern must appear. True randomness means that each outcome has an equal chance of occurring during each iteration of an event. That is, seven heads in a row does not change the 50/50 odds that the next coin flip will be heads too.
The first half of the book is filled with quick rules and explanations for examining randomness in a variety of situations.
Interesting tidbit: When vetting numbers, look at the second digits. They usually should be fairly well distributed if they are natural. Odd spikes of over usage are signs that the numbers may have been tampered with.