If your instructor tells you: “you cannot drive, you just can handle the car” it sounds arrogant but is in the most cases the truth. What he means is, that there are many rules you don´t know or you just take not serious enough. At least in the exam you will see he is right. Many other road user don´t stop at the stop sign, pass a solid line or are too fast.
But that´s not allowed for them as for you. A violation against applicable law does´n´t always mean an accident, but it always potentially dangerous. And if you make big or more violations it will let you fail your practical exam.
As in at the chapter “priority” it is important that you note the right things and take the right looks. Not just at crossings. You should see all signs and marks, should follow the rules and react on mistakes of other road user. If you look what others do it is not always the right thing. So better look by yourself what you have to do.