The real intention is revealed in the end

Toward the end of the Warring States Period (475－221 BC), there was a powerful state named Qin. It wanted to annex other states to unite China. In 228 BC, the Qin army conquered one of the states and prepared to attack another named Yan. So the Yan prince, Dan, sent a brave man called Jing Ke to assassinate the king of Qin.

战国末期，有一个很强大的国家叫秦国，它想吞并其他国家，统一天下。公元前228年，秦国的军队占领了其中一个国家。接着又准备入侵另一个叫燕国的国家。燕国的太子丹就派了一名叫荆轲的勇士前往秦国刺杀秦王。

In order to gain the confidence of the King of Qin, Jing Ke brought a map of the most fertile part of Yan territory for the king and hid a sharp dagger in it.

为了获得秦王的信任，荆轲带上了一张地图，上面画着燕国最富饶的地方，准备献给秦王。他在这张地图里藏了一把非常锋利的匕首

Jing Ke was allowed to present the map to the king in the palace. With great respect, he unrolled the map slowly. When it was completely unrolled, the hidden dagger appeared. Jing Ke grabbed it and stabbed at the king. But the king dodged the dagger and hid himself behind a big pillar. Jing Ke was then killed by the palace guards. His plan failed. Later, Qin wiped off Yan.

他来到秦国，见到秦王，恭敬地将地图献上，然后，慢慢打开地图给秦王看。当地图完全打开时，他抽出那把藏着的匕首，刺向秦王。但秦王躲开了，跑到了一根大柱子后。秦王的卫士们立刻跑来围住他，把他给杀了。燕国太子刺杀秦王的计划失败了。后来，燕国也被秦国吞并了。

People use the idiom to indicate that the real intention is revealed in the end.

人们用这个成语来比喻事情发展到最后，真相或本意就露出来了。