From The Quick and Easy Way to Effective Speaking by Dale Carnegie:

When Julius Caesar sailed over the channel from Gaul and landed with his legions in what is now England, what did he do to insure the success of his army?  A very clever thing: he halted his soldiers on the chalk cliffs of Dover; and, looking down over the waves two hundred feet below, they saw red tongues of fire consume every ship in which they had crossed.  In the enemy’s country, with the last link with the Continent gone, the last means of retreat burned, there was but one thing left for them to do: to advance, to conquer. That is precisely what they did.