Is being habitually honest a mental illness or a sign that one is developmently delayed?

Neither, quite the opposite is true.

Neither. Most likely a lack of self esteem.

Don’t most people strive to be honest? I love honesty, even brutal, for effective communication.

@KNOWITALL Does that include someone who gives TMI too much information?

@Red Sure why not.

It’s one thing to speak truthfully instead of lying. It’s another to blurt out things that are better left unsaid, like a three-year-old who can’t wait to tell you what her mommy said to her daddy in the bathroom this morning. Discretion generally comes with maturity. I don’t know which kind of honesty you’re talking about here, but some things are definitely better kept private. As a friend of mine used to say: “Don’t make everybody know your business.”

Since, as @Jeruba points out, discretion comes with maturity, the case of giving TMI could very well be due to arrested development. @RedDeerGuy1 , do you have in mind someone in particular?