Whenever I meet people and tell them what I do for a living, we inevitably end up talking about movies. Usually, people want to tell me about movies they’ve seen recently, or about their favorite movies, and they hope I’ll agree with them.

I usually do. I’m an agreeable guy.

Then I get the two questions every film critic gets asked: How many movies do you see in a week? And what’s your favorite movie of all time?

Now, these are not my favorite questions, mainly because my answers tend to disappoint people. They’re often hoping I see 20 movies a week, not five. And my favorite movies — films like “Queen Christina” (1933) or“Lady of the Night” (1925)— are ones most people probably haven’t seen.

Still, I want to make this clear: I’m pleased that people actually want to talk to me. And I totally get it — if I meet a dentist, we’re going to talk about teeth. If I meet a therapist, I’m going to practically lie on a couch and start whining about my father. When you know nothing about a person except for their job, you’re going to wind up talking about their job.

However, you should know that there is one thing you must never, ever say to a film critic, if you want to be taken seriously, you must never insist that a movie is terrible if you have not seen it.

That sounds obvious, right? I mean, who would do that? Well, actually, lots of people — and often.

For example, I recently spoke to a woman about a comedy I’d recommended. She said it was terrible. I was surprised, and then she added, “I watched it for five minutes and felt my brain cells dying, so I turned it off.”

Five minutes? That means she hadn’t seen the movie. Yet there was no dissuading her. She was sure she knew more than I did, even though she knew exactly nothing.

Of course, I understand that sometimes you’ll put a movie on and decide, on second thought, you don’t want to watch it. That’s reasonable. Sometimes you’re not in the mood or something might rub you the wrong way. But in that case, you must realize that in exchange for the relief of not watching the movie, you have forgone your right to have an opinion about it.

As a film critic, I am often in the position of generating opinions about movies I don’t feel strongly about. These are sincere opinions, but I have to come up with them based on seeing movies from beginning to end — the great, the horrible and all those in between. Often, especially with the in-between ones, I’d rather not have an opinion at all, but that sort of goes against the job description.

Perhaps as a direct result of this — of being paid, in a sense, to act like a know-it-all — I really don’t understand the pleasure taken in impersonating a know-it-all in daily life. I don’t get the joy of holding utterly baseless opinions.

I should add, baseless opinions are almost invariably negative opinions. Not once have I had someone say to me, “I haven’t seen that movie, but I know it’s wonderful!” Or “I watched five minutes and was interrupted, but already I know it’s a masterpiece!” Apparently, it’s only negative opinions that produce the endorphin rush of informed righteousness.

That sense of righteousness is an illusion. Clutching to one’s right to have an opinion based on nothing is wrong — and not only intellectually wrong. It strikes me as morally wrong. The damage it can cause may be minor when the topic is the relative merit of a comedy like “Mike and Dave Need Wedding Dates” (2016). But the consequences can be major when it comes to interpersonal relations or politics.

Yet all of us probably do this to some degree. Some do it a little, and some do it a lot. But when I catch myself doing it, I stop.

Seriously, until you’ve tried it, you don’t know how freeing it feels, how refreshing and clean it feels, to just say, “I don’t know.”

Reach Mick LaSalle: mlasalle@sfchronicle.com