“Some people work better with praise; some actually get motivated to work harder when they get chewed out. Now, how is that going to help me help my wife lose weight?”

We’re all fishers of men (and women and children) in our own little ways. We find ourselves campaigning for other people’s transformation, trying to get our kids to pick up after themselves or to tailor our partner’s behavior a bit more to our liking.

Some say we simply shouldn’t try to persuade each other: It’s a violation of people’s liberty. We have to learn to accept people as they are. You can’t change anyone; you can only change yourself. And it’s a persuasive argument — so much so, it’s easy to see that no one, not even those who decry persuasion, can keep from making persuasive arguments.

Mind Readers Dictionary: The Podfast : Play in Popup

Mind Readers Dictionary : Play in Popup

In practice, however, the notion that we shouldn’t ever influence each other is untenable bunkum. Influence peddling has been integral to life itself since the beginning. The boundary between living things has always been semipermeable. Biologists use the term “extended phenotype” for the way one phenotype (body) extends itself by persuading other bodies to do its bidding. In fact, if we didn’t extend our phenotypes, our bodies would lose a lot of weight. Eating is, in effect, a matter of influencing other organisms to synthesize proteins for us. Mating, too, is extended phenotype behavior, in the form of borrowing each other’s genes to pass our own on. In biology, sometimes the borrowing is one sided or parasitic; other times it’s mutual, as mating should be. Mutual is good. Helping people help themselves is always the most influential kind of persuasion.

Of course, there are times when accepting others as they are is the most productive attitude. Live and let live. It’s especially productive with people you neither can nor need to change — people you don’t live with, for example. Live and let live . . . elsewhere.

But when it comes to partners and kids, employees and colleagues, bosses and parents, we’re hooked on them and they on us, which increases both the prospect and the benefits of changing one another. We have credibility with each other — up to a point, anyway.

For we fishers of men, credibility is like test strength on our fishing line. Having a lot of credibility is like fishing with high-test line. Even clumsy tugging may still reel the other person in. Low credibility, in contrast, is like fishing with low-test line. Yank the other person around and the line will just break. And credibility waxes and wanes: We learn, through experience, whose judgment to trust.

In another essay, I talked about how learning is a two-step dance between reason and faith, between using experiences to forge new assumptions, and relying on those assumptions to predict new experiences. As an example, I discussed our desire for romantic partners to love our best traits so they’ll forge an assumption that we are wonderful, and wanting our partners to operate on faith in our wonders and ignore the decline of our best traits with age.

Being wonderful is one source of credibility, but the same learning logic applies to all sources. Credibility is an article of faith in someone, an assumption built up by recurring experiences of someone’s reliability. But even a wonderful partner can tug you just so much before you start wondering how wonderful that partner really is.

Children respond to your cajoling up to a point, but beyond it they begin to doubt your authority. It would be great to know where that point is — when, exactly, enough is enough — but because it depends on many factors, the best we can do is understand the dynamics, the interplay of factors.

Pulling enough but not too much is a challenge. It depends on your skill, and on your established credibility. It also depends on the weight of the fish you’re trying to reel in. And, of course, the fish is not really a fish; it’s another fisher of men, trying to reel you in, which makes the necessary skill that much more illusive. And if that weren’t complex enough, we each try to persuade ourselves as well, tugging ourselves in many directions with line that’s sometimes painfully high test or maddeningly low test.