7 +- 2

The issue with computer science (well, and all other engineering disciplines) is complexity.  We can't deal with how complex our "artifacts" are.  Our brains are built with a working memory size of about seven objects.  Maybe hunting parties, or family sizes, were seven?  Using any more of our brains to track more things was a waste and would lead to a loss of efficiency?  Is this why telephone number are seven digits long?  Don't know.  What I do know is that once something we're looking at has more than seven objects, we are incapable of understanding it.  More than seven visible variables, nesting levels, etc., and we can't understand what we're looking at.  Hence functional decomposition and object-oriented programming.  Most people whom claim to do OO, don't, but that's a post for another day.  For today, check out http://coloradmin.com/circle.html for a visual demonstration of the property.  Most people can only count to 7 (+-2) without having to "chunk" (group and then count).  See: http://en.wikipedia.org/wiki/The_Magical_Number_Seven,_Plus_or_Minus_Two for a more rigorous treatment of this.