When SVS is displayed on the PFD, even if SVS is not the "primary" terrain and attitude indication, it is compelling and difficult for a pilot to ignore. The "pilot's perspective" (AKA "ego-centric") view in a color pictorial speaks loudly compared to other displays and information. So the effect of its display of misleading information can be dramatic and strong. I have seen proof of concept demonstrations where the SVS was known to the pilots to have database errors and they still followed it. Human nature or as we call it "human factors". The advantage of SVS is how it can enhance the pilot's "situation awareness" also carries with it a vulnerability when it's wrong - it presents the wrong situation which is hard to dismiss.