My father was a close friend of Albert Einstein. As a shy young visitor to Einstein's home, I was made to feel at ease when Einstein said, "I have something to show you." He went to his desk and returned with a Yo-Yo. He tried to show me how it worked but he couldn't make it roll back up the string. When my turn came, I displayed my few tricks and pointed out to him that the incorrectly looped string had thrown the toy off balance. Einstein nodded, properly impressed by my skill and knowledge. Later, I bought a new Yo-Yo and mailed it to the Professor as a Christmas present, and received a poem of thanks.

As boy and then as an adult, I never lost my wonder at the personality that was Einstein. He was the only person I knew who had come to terms with himself and the world around him. He knew what he wanted and he wanted only this: to understand within his limits as a human being the nature of the universe and the logic and simplicity in its functioning. He knew there were answers beyond his intellectual reach. But this did not frustrate him. He was content to go as far as he could.

balance
n. condition of being steady 平衡
v. keep in a state of balance
properly
ad. really; completely 非常；完全地；正确地
impress
vt. have a strong effect on the mind or feelings of 给...深刻的印象
mail
vt. send by post
poem poet诗人
n. piece of writing in verse 诗
personality
n. character 个性
logic
n. the science or method of reasoning 逻辑(学);推理(法)
simplicity
n. the state of being simple; an absence of pretense 简单;简朴;单纯
function
vi. work