Once there was a man from the Chu Kingdom who brought a spear and a shield to the market for sale. He first raised the spear clenched in his fist and in a loud voice bellowed, "Comes one, come all and see the sharpest spear in the world, it can pierce any shield ever made !" People within earshot all came running crowding into see. Some even grabbed the spear and inspected its point. This person seeing all the people by his stall then took the opportunity and raised his shield saying, "Comes one, come all, the sturdiest shield in the world, no matter how keen the spear, nothing will pierce it !"
Standing by his side was a boy listening to the man's boisterous calls, "So what happens if your shield meets your spear ?" Dumbfounded the man gaped, then picking up his spear and shield walked quickly away.
We say and do things but we must base the on reality, not speak loosely, otherwise we will contradict ourselves.
Zhongguo Gudai Yuyan Gushi