I don’t understand why you think that honesty and candidness began in the 15th century. Please expand on your reasoning.
I wish I could expand on it with specifics. But I do remember hearing about this in a philosophy course. I wish I had paid more attention to it because later on the idea really intrigued me.
I think the meme
of honesty and candidness began to emerge when it did, in or about the 15th century, because of the growing commercial activity that was beginning to flourish at the time. It was something new, this activity, and a system had to be created to help facsilitate it. Society had to cultivate this meme if it hoped to establish lasting business relationships between people. I call it the networking
meme. Prior to this networking between people hadn't exist in sufficient amounts to make a difference. Without this meme and its evolution I don't think we would have the networking we have today.
Democracy is also a meme. (Democracy is also a networking meme or a meme of networking.) A meme, like a gene, is the means by which we inherit traits. These memes have pasted on the ideas of democratic behavior form generation to generation. Why some cultures don't practice democracy and have difficulty in accepting it is because the democratic meme, or network meme, was not part of their evolution or DNA
A meme, like a gene, instills in us a social behavior that comes naturally.