I dont agree. Ive been doing this for 8 years and the best gains i've ever made have been from not changing my routine. In the past 9 months i have decided to stick with one solid routine and gained 50 lbs from it, with no "confusion" or switching lifts and no platue. My chest grew 8 inches my arms grew 2 as well as my foreamrs and claves and my legs gre 7 not to mention my strength gains. I firmly belive in consistency. if you platue i personally doubt its from "not switching it up". i think it because of the routine or diet. If you have a solid routine, plenty of rest and enough calories you should be able to push yourself hard enough in the gym to make gains week by week, month by month. i rarely see people sticking to a routine longer than a few months, and with that said i also rarely see people with physics in which i am impressed by.
Honeslty I think diet and nutrition matter more than anything. Sorry if I sound bitter I just hear all too many guys saying "Switch it up!" when thats not always the best scenario.
Best advice: test/experiment and get to know your body. Learn what works for YOUR body, not ours