He helped his rival, but he only nourished a viper in his bosom.
nourish a viper in one's bosom
idiomTo do acts of kindness that will be met with ingratitude and will cause one harm in the end.
Origin
disputed originFrom Aesop's fable The Farmer and the Viper.
By giving the dishonest employee a promotion, the manager realized he had nourished a viper in his bosom.
The king showed mercy to the captured rebel, never suspecting that he had nourished a viper in his bosom who would eventually lead the coup.
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abound in one's own sense
To follow one’s own inclinations and opinions.
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ace up one's sleeve
A surprise advantage of which others are not aware.
- 03
act one's age
To behave in a manner appropriate to one's age.
- 04
act one's age, not one's shoe size
Synonym of act one's age (“to behave in a mature manner; to avoid being childish”).
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afraid of one's own shadow
Exceptionally timid.
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air one's dirty laundry in public
To reveal one's sordid secrets to the public.
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air one's dirty linen in public
Synonym of air one's dirty laundry in public.
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albatross around one's neck
A characteristic, possession, associate, or previous deed that hinders one's ability to succeed.