Well, it's not everything about Gesso. This article is very good. In a future Blog or Forum post I'll have something for your on the light scattering capability of quality gesso and why you absolutely need to gesso every canvas you ever use with a quality coat or two. Never paint with a canvas, even one that claims to be primed. Trust me, whatever gesso they used on it was low quality unless you are buying the ones we recommend to you.
https://www.marthastewart.com/7973502/gesso-paint-primer-explained