How to win friends and influence people” has a flip side: “How to lose friends.” One of the easiest ways is by sticking to one's convictions — or, at least, by sticking to them while making them known. There can't be many readers who have never lost a friend or, at least, annoyed someone dear by maintaining a principle and conforming their actions to it.

Your Uncle Filbert abandoned his wife, got a civil divorce, and now is intending to marry someone else. Do you attend the wedding to please him, even though, by doing so, you may give others the impression that you see nothing wrong in what he is proposing to do — enter a state of adultery? Or do you decline to attend on principle, knowing that your relationship with him may be damaged?

If people were as open-minded as they profess to be, Uncle Filbert would take no offense at your staying away. He would receive gratefully your explanation of why you will be unable to attend his wedding. While disagreeing with your calculus, he would respect you for abiding by your convictions, and your relationship with him would suffer no long-term damage. Of course, it almost never works out this way. He will conclude that someone who doesn't approve of each of his actions doesn't approve of him at all.

Some people, in flipping open the New Testament, have a way of finding no verse other than John 17:11: “that they may be one, even as we are one.” For them, the chief message of Scripture is oneness, commonality, agreement, unity. The impulse is understandable. Most of us wish to avoid contention and the uneasiness that even shallow disagreement can bring. We want to get along with everyone, and we want everyone to get along with us. We recognize that there will be a multiplicity of opinions. We may have little hesitancy in highlighting our own opinions when it is a matter of disagreeing with strangers, but it seems another thing altogether when the disagreements may be with friends or family. When that prospect looms, we want to focus on unity, even if that means never alluding to some things.

A relative of mine has a friend from childhood who, some years back and after a marriage and a child, “discovered” that she was a lesbian. My relative hasn't allowed that revelation to cloud their friendship. The other woman and her female “companion” are welcome at my relative's home.

Living by principles would result in no division if everyone agreed on the principles, but theydon't.

A year ago a family reunion was planned. It was intended for family members only, but my relative invited her lesbian friend and that friend's “companion” on the excuse that, at least to her, the two were “just like family.”

Not to me they weren't. I explained that I hadn't known her friend since the two of them were teen-agers; I certainly wouldn't recognize the woman on the street if I saw her today. She wasn't “just like family” to me. I said she and her “companion” shouldn't have been invited to a family event.

Besides, I noted — and this is where I got into trouble — I didn't want my son to get the idea that his mother and I could approve of that kind of relationship. If the friend and her “companion” showed up at the gathering, we certainly couldn't argue with them or ignore them, and yet our civility might lead our son to the wrong conclusion.

That didn't go over well with my relative. I had stated my principle, but she didn't like it. She thought there was something wrong with me because I thought there was something wrong with her friend. I wasn't sufficiently “live and let live.” (As it turned out, the friend and her “companion” ended up being disinvited.)

This situation brings to mind other verses that round out the picture. “I have not come to bring peace, but a sword” (Matthew 10:34). “Henceforth in one house there will be five divided, three against two and two against three; they will be divided” (Luke 12:51). Why a sword, why divided? Because of principle. Living by principles would result in no division if everyone agreed on the same principles, but the fact is they don't. The only way to effect unity is for one side or the other to convert. Normally this does not happen, which leaves two alternatives if one wants to try to save a relationship: learn to live with the disagreement or pretend there is no disagreement. The second choice means to live a fiction, at least with respect to this subject and these persons.

The sword, in cutting, unavoidably cuts both parties. I found that out with my relative. I thought my principle — which happened to be anything but a novelty, since the whole world accepted it until a few years ago — was easily understood and, if not believed in by some, at least could be accommodated readily. I learned a lesson — the hard way.

Karl Keating is founding director of Catholic Answers.