Confusion in validateWrite() method

Hi everyone,

I am having one table i.e. CarTable. In this table I have CarId and I set its Mandatory property to Yes. Now, I am inserting one record through the following job:

 static void InsertMethod(Args _args)
{
    CarTable            carTable;
    ;

    //Initialize the table variable
    carTable.initValue();

    //Write some values to the table variable
    carTable.CarId = "500";
    carTable.CarBrand = "Audi";
    carTable.Model = "A4";
    carTable.ModelYear = 2009;
    carTable.Mileage = 0;

       
    if(carTable.validateWrite())
        carTable.insert();
}

Now, validateWrite() will validate all the fields before insertion.  It means, suppose if I am not using validateWrite() method then it wil allow me to insert the record without giving any value in CarId field?

It should not through any error, if I am inserting the record without CarId field but it is, why.