I was the quiet, reserved. extremely shy, introverted middle child. One day I overheard my grandma say to my mom in what sounded like a warning voice, "You better watch her Clover." she said, "You know "still, water runs deep." The phrase "still waters run deep" is an idiom that means a person who appears quiet or calm on the surface may have great depth of character, knowledge, or emotion. It suggests that there is more to someone or something than meets the eye, and that beneath a calm exterior, there may be profound thoughts or feelings. When grandma warned my mom about me, she made it sound ominous. I took it to mean "You better be careful of her and watch your back. She is unsafe." I remember thinking, "I don't want to be still water." I remember for years worrying about being still water.