I've wondered casually about this before, but never really put much thought in it. Which is odd, because it's really a quite intruiging subject.
Modesty (Tact) is commonly accepted as a good and fair trade to ones skills. Yet modesty in itself implies that the honest true underlying thoughts are merely being surpressed and sugar coated. And thus, the skill of modesty is nothing more than deception. A way to cover up truth. A widely accepted and appreciated method of lying.
To be modest is to project your thoughts in more subtle and generally nice ways.
But why is it so appreciated then, specifically in relationships? No one enjoys being lied too. Everyone wants people to tell the truth. Yet when one modestly coats it with the term modesty, it's all fun and flowers.
Is it a mere matter of perception, or are people truely that easily decepted by what they're told and taught. That common knowledge about modesty being a good thing is enough for them to accept it so?
If interested, I am not a modest person. Except when dealing with customers and from a business point of view, when I see that being modest is rewarding. Whereas on a more personal level, and the most personal level being a monogamous relationship. I would not dare to fall for modesty. I would not dare to fraud and deceit the way I do around the common consumer.
edit: Revised, Modesty -> Tact.