I've never understood how any being can effectively suppress its emotions. For real life humans, this is obviously pathological.
But for Vulcans, maybe Surak discovered that Vulcans held an innate ability to maintain emotional control, which Vulcans in later times discovered via neurological analyses/studies.
huh? There are various Human religions and philosophies(Buddhism and Stoicism come to mind) that teach emotional suppression as the path to inner peace or enlightenment. Granted they're not as extreme about it as the Vulcans, but it's not some rare kind of concept.