When you use Mesora in an argument it is either as a defense or in reference to an undisputed Mesora. Nobody can demand that you agree to him because of something you don’t agree to or know about. But, he might be pointing out to pay attention to how things were always done, hence Mesora.
This is an argument used often in Gemara. When proposing a Shita we would ask how it can be if we all never heard of it, or Hanach Lahem Liyisroel, or Sha’al Avicha Veyagedcha.