如果你沒辦法解釋給六歲孩童聽，表示你自己根本沒搞懂。 If you can't explain it to a six year old, you don't understand it yourself.

如果你沒辦法解釋給六歲孩童聽，表示你自己根本沒搞懂。
— 亞伯特．愛因斯坦（Albert Einstein），相對論之父
If you can't explain it to a six year old, you don't understand it yourself.