Q:

"Naive" Vs "Simple"

According to the dictionaries, simple means: 
foolish; easily deceived: 

He’s a very simple young man. 

And naive means: 

a very simple person!

Cambrige Dictionary defines naive in the following way:

Too willing to believe that someone is telling the truth, that people's intentions in general are good, or that life is simple and fair. People are often naive because they are young and/or have not had much experience of life.

It is vague now! To me they meant the same, but I guess there is something missing here that I don't know! How can I differentiate between them?
How do you interpret them?

A:

"Simple" is used in a number of different contexts. When applied to a person, it is a more polite way of saying "stupid." It means a person's brain doesn't work that well, irrespective of that person's experience.
On the other hand, a "naive" person does things that may seem stupid because of a lack of experience. A naive person tends to be innocent and have an overly positive expectation in circumstances that are not that positive. In particular they trust where they should not and believe what they are told. There's no reason to think a naive person is stupid, only inexperienced and probably sheltered.

