“Human memory for sequences is temporally limited, with a short term
capacity of around seven, plus or minus two items. In addition, when
humans do remember a sequence of items, those items be familiar chunks
such as words or familiar symbols. Finally, human memory thrives on
redundancy-we’re much better at remembering information we can encode
in multiple ways”
http://cyberforge.com/weblog/aniltj/archive/2004/10/14/689.aspx