to feel just like a fish in water
如鱼得水
In the late Eastern Han Dynasty， the country was in confusion.
东汉末年，天下大乱。
In order to reunite the country， Liu Bei paid a visit to Zhu Geliang who had hidden himself in the countryside.
刘备为统一天下，特意拜访隐居的诸葛亮寻求帮助。
He went there twice but didn‘t see Zhu Geliang. Then the third time he finally met him.
他连去了两次都没见到诸葛亮，第三次才见到了他。
Liu Bei explained why he came and explained his noble ambition to Zhu Geliang.Zhu Geliang also proposed some very good strategies.
刘备说明来意，并畅谈了自己的宏图大志。诸葛亮也提出了周详的战略方针。
After listening， Liu Bei was so happy， he appointed Zhu Geliang as his military advisor.He said: “Zhu Geliang to me is as water is to fish.”
刘备听后大喜，于是立诸葛亮为军师。他说：“我刘备有了诸葛亮，就好像鱼儿有了水一样。”
With the assistance of Zhu Geliang， Liu Bei‘s power expanded rapidly， and finally he realized his goal.
刘备在诸葛亮的帮助下，势力不断扩大，最终实现了目标。
Nowadays， this phrase is often used to describe the person who stays in the environment which suits him/her perfectly， or someone who is very adept at using the suitable or right methods.
如今，这个短语常常被用来形容一个人处在完全适合自己的环境中，或者一个人能够熟练地应用合适的或正确的方法。
【文化链接】
“如鱼得水”用英文可以表达为“feel just like a fish in water”，我们来看一个例句：
I‘ve wanted to study at Beijing University my whole life. I also love the culture and the weather in Beijing. I feel just like a fish in water.
去北京大学学习是我一生的梦想。我还喜欢北京的文化气氛和天气。我在北京简直就是如鱼得水。