If by must you mean often tend to, and by relationships you mean ratios, then I agree; it's a very useful model in the absence of other information. Wonderful, in fact.<p>Still, sociologically, working scientists tend to believe in these models as if they were hard rules, to the extent of constructing bridges, rockets, nuclear reactors, nationwide health recommendations and global financial systems without fundamentally understanding why each distribution might arise, and why it might fail to explain real phenomena.