Pat - I'm reminded of what the Roman critic Horace wrote way back in 30 BC or so: "A play should not be shorter or longer than five acts". Well, for centuries and centuries playwrights followed that pattern -- notably (and most memorably and to great effect) Shakespeare. Then in the 1800s, another critic went into more detail and described those five acts as: exposition, rising action, climax, falling action, and revelation -- and again, that pattern has proven to resonate deeply. In other words, the 5 act structure, like the great gca templates, simply works. . Now, some might suggest that we've simply grown accustomed to play structures and templates; but I think that it's not that we've gotten used to the patterns, but that such Patterns pre-exist and are functions of the art forms themselves (and perhaps even of our human psyches) and that they made themselves manifest as soon as artists became conscious of their art -- for plays, back in 30 BC; for gca, around 1910.
Peter