  The trick is to look first at the interactions of nearest constituents.  Then one moves to a block of constituents as it relates to nearest similar blocks.  The new block-to-block interaction can sometimes be obtained by a “scaling” of the original individual constituent interaction.  One continues this process to the limit of an infinite system and looks for a limit point to the continually rescaled interaction.  From this limiting behavior the surprising “universal” features of the phase change can sometimes be found, explaining the generality of similar phase transitions over diverse physical systems.