I believe it may be a mask...? This is due to the fact that people like to wear a "mask" (metaphorically speaking) to fake their happiness and hide their sorrow, but other people do not realize that they are faking it. Also, the "thief" part may be representing the person who wears it, as they are kind of stealing other's worries away so they won't have to worry about them, if that makes sense. And the toy of queen may mean how it's usually the people who are most respected fake their happiness, like how they say the funny friend is the most depressed. And the giving all likeliness borrowed is more about faking emotions.
