You see, everyone in the world gets their chance to have the Holy Spirit open their eyes to their need of a Savior. (John 1:9) And everyone gets their chance to bow their knee before that Savior, accepting salvation as a gift, through faith.
But not everyone accepts that gift when they get that chance. Some people simply blaspheme the Holy Spirit by saying, either out loud or quietly in their hearts, “No…I will not admit I need a Savior. No…I will not believe in Jesus”.
And that sin cannot be forgiven.