A watched kettle never boils的用法和样例：
- A watched kettle never boils.
- Don't you know a watched kettle never boils? Whether they're late or early,looking out of the window won't bring them here any quicker.
- A watched kettle [pot] never boils.
- I have been waiting for that paint to dry for two hours now. How it is that a watched pot never boils?