张良是战国时期韩国的后代。
秦国灭了韩国后，张良想要用他的家产找到勇士去刺杀秦王，为韩国报仇。
他的弟弟去世时，他也没有好好安葬，因为他的祖父和父亲都是韩国的宰相，曾经辅佐过五个国君。
后来，张良找到了一个大力士，并制作了一个重达一百二十斤的铁椎。
当秦始皇到东方出游时，张良和大力士埋伏在博浪沙这个地方，想趁机袭击秦始皇，但是他们误击了侍从的车。
秦始皇非常生气，在全国范围内搜捕刺客。
于是张良就改名换姓，逃到了下邳躲藏起来。
有一天，张良在下邳桥上散步时，遇到了一位穿着粗布衣服的老人。
老人故意把鞋子掉到桥下，并让张良帮他捡上来。
张良虽然很惊讶，但还是忍住怒气，走到桥下帮他捡鞋。
然后，老人又让张良帮他穿上鞋。
张良觉得这很奇怪，但他还是照做了。
老人穿好鞋后笑着离开了。
张良目送他离开，感到非常惊讶。
老人离开了一段距离后又返回来，对张良说：“你真是孺子可教啊！五天后天刚亮的时候，来这里和我见面。”
张良答应了，五天后的黎明，他按照约定来到了桥上。
但是老人已经在那里等他了，他生气地说：“跟老人家有约，你怎么迟到了？”
老人离开了，并告诉他五天后再早点来。
五天后公鸡刚啼叫，张良就去了。
可是老人还是先到了，他又生气地说：“你又迟到了！”
老人再次离开了，并告诉他五天后再早点来。
五天后，张良还没等到半夜就来到了桥上。
不久，老人也来了，他高兴地说：“这就对了。”
然后拿出一本书，告诉张良这本书可以让他成为君王的老师，十年后就可以发迹，十三年后可以在济北见到他，谷城山下的黄石就是他。
老人说完这些话就离开了，从此以后张良再也没有见过这位老人。
等天亮一看，原来老人给的书是《太公兵法》。
张良认为这是一本特殊的书，就开始研读它。
后来，张良利用书中的兵法帮助刘邦建立了汉朝，那位老人就是黄石公。
而“孺子可教”这个成语就被用来赞扬可以教导造就的年轻人。
Zhang Liang was a descendant of the Han State during the Warring States period.
After the Qin State destroyed the Han State, Zhang Liang wanted to use his family's wealth to find warriors to assassinate the Qin Emperor and avenge the Han State.
When his younger brother passed away, he did not give him a proper burial because his grandfather and father were both prime ministers of the Han State who had served five kings.
Later, Zhang Liang found a strongman and made a 120-jin iron hammer.
When the First Emperor of Qin traveled to the east, Zhang Liang and the strongman ambushed at Bolangsha, intending to take advantage of the opportunity to attack the First Emperor of Qin, but they mistakenly hit the chariot of the attendant.
The First Emperor of Qin was furious and searched for the assassin throughout the country.
So Zhang Liang changed his name and hid in Xuzhou.
One day, Zhang Liang was walking on the bridge in Xuzhou when he met an old man wearing coarse clothes.
The old man deliberately dropped his shoes under the bridge and asked Zhang Liang to help him pick them up.
Although Zhang Liang was surprised, he held back his anger and went down to the bridge to help him pick up the shoes.
Then, the old man asked Zhang Liang to help him put on the shoes.
Zhang Liang thought this was strange, but he still did as he was told.
After the old man put on his shoes, he smiled and left.
Zhang Liang watched him leave, feeling very surprised.
After leaving for some distance, the old man returned and said to Zhang Liang, "You are indeed teachable. Meet me here five days from now at dawn."
Zhang Liang agreed, and at dawn five days later, he came to the bridge according to the agreement.
But the old man was already there waiting for him, and he scolded, "If you have an appointment with an elder, how can you be late?"
The old man left and told him to come earlier five days later.
Five days later, when the rooster crowed, Zhang Liang went.
But the old man was still ahead of him, and he scolded again, "You're late again!"
The old man left again and told him to come even earlier five days later.
Five days later, Zhang Liang came to the bridge before midnight.
Before long, the old man also came, and he happily said, "That's right."
Then he took out a book and told Zhang Liang that this book could make him a teacher to the king, and in ten years he would rise to prominence, and in thirteen years he could meet him at Jibei in the north of Gucheng Mountain, where the Yellow Stone was located.
After saying these words, the old man left, and Zhang Liang never saw him again.
When it got light, it turned out that the book the old man gave him was 'Taigong's Art of War'.
Zhang Liang believed that this was a special book and began to study it.
Later, Zhang Liang used the strategies in the book to help Liu Bang establish the Han Dynasty, and that old man was the Yellow Stone Elder.
And the idiom 'teachable youth' is used to praise young people who can be taught and trained.
