First of all, explain the reason why Einstein met with Truman: when the United States successfully developed the first atomic bomb in human history, the US Congress began to discuss whether to use the atomic bomb against Japan, and finally agreed with an overwhelming number of votes. Through the proposal of dropping the atomic bomb, it was decided to take the lead in using nuclear weapons against Japan, and it was Truman who gave the order later.

So Einstein, who learned the news, immediately decided to hold talks with Truman before he officially gave the order, hoping to stop the United States from dropping atomic bombs on Japan through his own lobbying. The two met as scheduled, and Einstein explained to Truman the seriousness of dropping the atomic bomb and the huge risks it needed to bear from many aspects, such as "the explosive power of the atomic bomb, the huge casualties it may cause, and the historical responsibilities it carried".

After listening to Einstein's narrative, Truman looked solemn and lost in thought. Soon, he faced Einstein with the same serious expression and asked two questions: First, do you know how heavy the casualties of frontline soldiers are? Secondly, if you don't use the atomic bomb and end the war as soon as possible, can you predict how many young soldiers will die on the battlefield?

Faced with these two extremely heavy problems, Einstein hesitated many times and finally had to choose silence. This matter is of great significance to Einstein himself, because the successful development of the atomic bomb can not be separated from his formula of conservation of mass, so he deeply believes that if the atomic bomb, a unique and powerful weapon in human history, is made through the theory he discovered, then he will have an unshirkable responsibility for the people who died because of it, but in the face of the tense situation at that time and the young life who kept going to the front because of the war, he finally chose silence.