We all communicate “Do as I say, not as I do” to our kids in one way or another.

Sometimes, it’s not such a bad thing. We hope our children won’t make the same mistakes we made in life, and we want them to do better than we did, so it makes sense that we want them to do things differently. “Yes, I smoke, but you’re not allowed to” is not simple hypocrisy, especially if you follow up with something like, “I made a bad decision when I started, I realize it’s not good for me, and I’m trying to quit. You’ll never have to face this problem if you never start.” Also, for many behaviors, children ought to wait to until the appropriate age, so it’s not inconsistent to say, “Do as I say” (no makeup, violent video games, staying out late, owning a car) “and not as I do” (all of those) but with an added phrase such as “until you are older,” “until you can pay for it with your own money,” or “until you can take care of yourself.”

But “Do as I say, not as I do,” when it does take the form of inconsistency, can also undermine your intentions as a parent. Think of the mother reclining in her beach chair who bellows to her distant kids, “You guys stop making so much noise and bothering everybody!” or the father who regularly spanks his son for hitting his sister, or the couple who routinely curse a blue streak around the house and punish their children for swearing. If you’re a parent, you’re probably conducting a swift mental review of your own behavior for similar, if less dramatic, inconsistencies. And if you’re honest, you’ll find them. Why does it matter?

The research points to three consequences of inconsistency. First, the effects of your teaching are diminished when deeds and words are not in line. The more inconsistent you are, the more you will hear yourself saying, “How many times have I told you not to do that?” Second, children can readily recognize inconsistencies, and they become more upset with their inconsistent parents than children who have parents who are more consistent. And although even small children can readily report on parental inconsistencies, they usually wait until adolescence to throw them in their parents’ faces. Third, a parent who does one thing but expects or demands the opposite from a child is more likely to have discipline problems and more likely to punish a lot in the effort to overcome the influence of his or her own modeling.

The main idea to bear in mind here is that modeling—teaching by example—affects behavior far more than telling your children what to do (and far more than punishing them, too). Even when young children have to do what their parents tell them to do, they may well intend to do what their parents actually do as soon as they can get away with it. If you make your kids use seat belts, helmets, and sunscreen but you don’t model these safety behaviors yourself, they’re more likely to let such precautions slide as they grow up and take charge of themselves. Most modeling influences are tacit. The parent does not have to say “Watch this” or “This is how you carry yourself in the world.” The child just learns by observing. He does not have to understand what the parent is doing in order for the learning to take place.

Brain research has demonstrated that there are special cells called mirror neurons. When we watch someone do something, our mirror neurons become active in the brain as if we ourselves were engaging in the same behavior we are observing. This suggests that learning consists of making connections not only in a figurative way (as we assemble sequences of behavior) but also in a literal way, as observation of a behavior forges the same neural connections made from practicing that behavior. Let’s say—not that this is true of anyone who reads Slate, of course—that while you never give other drivers the finger when your spouse is in the car, you’ll do it when the kids are in the back. Just picture the little darlings, strapped snugly into their car seats, raising their own middle digits every time they see you do it. Thanks to mirror neurons, they’re getting lots of bird-flipping practice back there without moving a muscle. Remember this in a few years when they start doing it to one another—and to you, of course, which will fill you with baffled rage and a desire to chastise them in innovatively harsh ways.

Modeling does not always dictate a child’s behavior—your kids won’t inevitably do everything you do—but it’s an important and underappreciated way to transmit information, experiences, skills, beliefs, values, and large segments of behavior. Modeling can teach a child how to handle conflict, react to stress or fear, or interact with others. It’s unforgiving in that it teaches your best and worst behaviors, the ones you’re most careful to practice and others you’re barely conscious of. One way to test the power of modeling is to play a game with your child in which you imitate each other. Pretend that you (as your child) broke something, returned home with poor grades, or committed some other plausible offense; ask your child, playing you, to respond to the news as you would. These renditions are usually uncomfortably accurate and nuanced, and yet our typical first reaction is “I never do that.”

A certain degree of inconsistency in modeling and its relationship to what you say is inevitable. You are not the only model in your child’s life: There are other relatives, peers, teachers, peers’ parents, media characters, and so on. You’re modeling one way to respond to stress, for instance, and Hellboy and Hannah Montana are modeling others. In two-parent households, the two adults will model different behaviors and ways of being in the world. Sometimes the discrepancies are large—for example, when one parent lives on junk food and the other inveighs against this habit. This is a normal level of inconsistency for family life. It gets more complicated when you add to the mix other relatives in the home, separated or divorced parents with new partners, and the like, but children have to cope, and they usually do. After all, doing one thing but saying something else to your child is the important tip of a larger iceberg, a larger set of common inconsistencies that go far beyond child rearing. It’s only human.

While inconsistency may be inevitable, parents can still take steps to reduce its effects on their kids. If you’re interested in practical parenting advice along those lines, please click here. We cannot appear to our children as saintly fictional characters who model only desirable behaviors, but an appreciation of the potency of modeling can help us set an example for them with a little more purpose and effectiveness.