Understanding is rediscovering

Understanding a concept should be rediscovering it all by yourself. When you say you understood some scientific article you read then you should be feeling as if you discovered the concept all by yourself.
When you say you understood gravity, you should be able to come up with the equation for the gravity from the basic understanding of the fundamentals. When an apple falls on your head, will you be able to come up with the same equation for gravity as Gm1m2/d^2 ?