Question regarding sanity

Hi my name is latrine and i have a question regarding sanity How does one know if one is sane or if one is insane? Does one realize that one is not making sense when one speaks or does one think the masses think that one is not making sense

Vice Versa!

Well for me , A person who can't keep a secret also say words without thinking about what will happen next.... To be honest a person who act in a silly way is insane lol