Is sadness a flaw?
Flaw can be used as a noun to represent a defect in something. E.g. The car had a flaw that caused it to crash. Flaw can be used as a verb. E.g. Not following the recipe can flaw the end product. You'll commonly see it in the past tense... E.g. Your view of the world is flawed. Flaw can also be a noun meaning a gust of wind or windstorm. Also known as a "windflaw."
Yes, you can see sadness in someone's eyes. I have seen it in the eyes of a man who keeps running from love and relationships. He would never explain what is it that bothers him, but he is full of sadness... I felt sorry for him, this sadness is pervasive and reveals something about his troubled soul... Can't explain how I see the sadness, i just do, it is there.
Flaw: noun: a small often hidden defect; anything that does not work as intended. verb: to make or become defective. Example sentence: The space shuttle Challenger exploded during liftoff due to a fatal flaw in an O-ring on the solid rocket boosters. There was a flaw in the heating unit. The computer contained a security flaw that had to be fixed. The prosecutor found a flaw in the defendant's statement. The teacher passed out a…