Someone habitually exaggerates the merits of undistinguished people or things.
The goose is proverbially contrasted with the swan as being the clumsier, less elegant and less distinguished bird.
cook his goose
spoil someone's plans
cause someone's downfall – informal
The underlying idea of this phrase seems to be that a goose was cherished and fattened up for a special occasion and therefore to cook it prematurely meant to spoil the plans for a feast.
kill the goose that lays the golden eggs
destroy a reliable and valuable source of income.
One of Aesop's fables tells the tale of a man who owned a miraculous goose that laid eggs of gold. However, he grew dissatisfied with its production of just one egg a day and killed it in the deluded expectation of finding a large quantity of gold inside it.
1999 - New York Times - Change is needed in the nation's drug policies. But we need to address the problem carefully in a way that doesn't kill the goose that lays the golden egg.
What is sauce for the goose is sauce for the gander
what is appropriate in one case is also appropriate in the other case in question – proverb
This expression is often used as a statement that what is right or wrong for one sex is right or wrong for the other as well.
John Ray, who was the first to record this saying (in his English Proverbs of 1670), remarked - This is a woman's Proverb.
1998 - New Scientist - What is sauce for the US goose is sauce for the Iraqi gander!