Generally, if someone tells you something is “in your blood,” that person means you possess, or are likely to possess, a particular trait because another person in your family possesses it. Usually, the family member is older, like a parent or grandparent. This trait can be anything from athletic ability to business savvy. Since the trait can be positive or negative, saying it is “in your blood” can act as a compliment or insult. Often, this saying carries the unspoken implication that whatever the trait is, it is unchangeable or the likelihood that you can or will change it is slim.
Sometimes, people use the saying “in your blood” in a positive, complimentary way. For example, someone might say the daughter of a successful business owner will eventually succeed with her own business because it’s in her blood. Even if this person has shown no inclination toward or skill for business ownership in the past, some people will assume she will be successful at running a business because her father is successful at running a business.
Other times, people can use the idiom “in your blood” to point to the presence of a negative trait shared by two people. For example, people might say the son of a convicted felon will likely go to jail himself because it’s in his blood. People expect that the son will follow in the father’s footsteps, whether the reasons are related to nature or nurture.
Often, people associate the idiom “in your blood” with permanence, regardless of the positive or negative nature of the trait. The daughter of the business owner might not impress investors during the first year of her own start-up company, but the likelihood that she will ultimately succeed seems certain because it’s in her blood. Likewise, the son of the convicted felon might only have one speeding ticket on record, but people might expect him to go to jail soon because it’s in his blood.
Similar to physical traits, personality and character traits often are shared by family members. This makes it easy to understand why “in your blood” rings true for some people. Still, like other idiomatic expressions, there are situations when this one applies and situations when it doesn’t apply. When using this saying, a speaker can only point out trait similarities, or the possibilities of similarities, with any real confidence. It’s not feasible to say something is in another’s blood and expect the statement to be treated as fact.