Napoleons loss

Even though Napoleon lost he is still a good leader. But what I dont get is why he would send 422,000 people into russia all at once. He could have sent as many troops as the russians had or just a little more that them just incase something happened. The russian army was to strong so they had to retreat and go all the way back to France and then when they got back they only had about 10,000 people left and the army wasnt as tough.