why subclass reference can't hold superclass object in java

Question

class One{

}
class Two extends One{

}
class Main{

      public static void main(String[]  args){
       Two t = new One(); // invalid 

}`
}

I a

Answer 1

Because a dog has all the behaviours of an animal, but something that is only known to be an animal is not guaranteed to have all the behaviours of a dog.