know which side bread is buttered on
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know which side (one's) bread is buttered (on)
To know how to best ensure one's success. I know which side my bread is buttered on, so I was very nice to the recruiter and promptly sent her a thank you card after our interview.
know which side one's bread is buttered on
Prov. to be aware of where your money comes from; to be loyal to the person or thing that will benefit you the most. Wife: Please be sure not to upset Grandma. You know we can't do without the money she sends us every month. Husband: Don't worry. I know which side my bread is buttered on.