After somebody threw a flask of acid on the Mona Lisa in 1956, they put her behind bulletproof (and presumably acid-proof) glass. Same with Picasso's Guernica, after a man spray-painted "Kill all lies" in giant red letters across the canvas.

I have always found it unbelievable that most very famous paintings have no physical barrier between them and the visitors. At MoMA in New York, I wandered around a small wall, turned, and was alarmed to discover Starry Night by Vincent van Gogh, hardly more than an arm's length away from my distracted, clumsy body.

The hundred-million-dollar painting is protected only by a line of tape on the floor about two feet from the wall, presumably marking the distance at which your communion with the painting becomes too intimate and the security guard must lean in and scold you.

The vast majority of famous artworks on display are protected only by similar lines of tape, shin-high string fences, or in more extreme cases, velvet ropes. Amazingly, these non-barriers are sufficient to keep the vast majority of gallery visitors from mucking with the world's most valuable art. None of these boundaries could stop a determined vandal, but they do seem to prevent nearly 100% of the rest of us from getting inappropriately close. (The guards would quickly tackle you of course, but I'm pretty sure they aren't allowed to tackle you before you start clawing at the artwork.)

The truth is most people don't want to muck things up, at least in a premeditated way. But when there are absolutely no boundaries, no lines to indicate when your proximity to some delicate thing becomes inappropriate, people will end up mucking things up. It's just what we do.

The classic velvet rope fence, drooping between portable silver posts-the kind that shapes cinema queues, demarcates staff-only areas, and protects unattended wedding cakes-is the quintessential "polite barrier." It's so determined not to offend you that it's actually made of velvet. It doesn't want to imply bad intentions on your part, the way barbed wire or pointy wrought iron fences do. It only wants you to consider kindly moving alongside it rather than across it.

Velvet ropes can't stop anyone physically, but somehow, they stop almost everyone psychologically. This is a useful principle for guiding one of the most important clumsy, wandering people in your life: yourself. You can use the guiding power of the velvet rope to gently shepherd yourself away from moments in your routine where short-term impulses sometimes undermine your bigger goals.

It's strange when you think about it, but self-control isn't a trivial matter. For some complex evolutionary reason, it is mysteriously difficult to get ourselves to do certain obviously helpful things, such as flossing, and get ourselves not to do unhelpful things, such as eating a cookie immediately after flossing. (The specific challenges vary from person to person.)

We do self-defeating things like this because we have conflicting desires. We want good teeth and we also want late-night cookies. Usually we understand which path is smarter and ultimately more rewarding, but getting ourselves to take that path, especially on a consistent basis, can seem like a real puzzle.

The usual impulse is to control ourselves, with force if necessary. We make sweeping declarations about how we're going to behave from now on (usually starting next Monday). No more junk food on weekdays! No more internet before lunchtime! A new sheriff is in town!

Predictably, we rebel-at first by sneaking in glorious, naughty exceptions to our self-imposed laws, and then by abandoning the rules completely, once it's clear that we can't simultaneously be the legislator, the police, and the perpetrator.

More and more, when it comes to getting away from unhealthy habits, I'm using a velvet rope approach instead of a more forceful, "barbed wire" approach. I place some sort of gentle, symbolic barrier between myself and the thing I want to stop doing, and often it's enough to break the momentum of an unfolding poor choice.

For example, one dumb thing I have a history of doing is drinking coffee in the late afternoon, despite the well-established risk of tossing and turning all night. Still, out of some stubborn, reptile-brain pattern, I'm frequently tempted to do it.

I have no doubts at all that if a tiny square of velvet ropes were to appear around my coffee grinder every day at 2pm, I would almost never make the wrong choice.

A similarly tiny, razor-wire fence would be too much. I'm not a monster; I just end up bargaining with bad impulses sometimes. A modest, velvet reminder to direct myself elsewhere is all that would be needed to keep me on a better path.

I don't have tiny velvet ropes, so instead, after my post-lunch coffee, I immediately place the grinder's removable plastic reservoir into the sink, to be washed with the dishes later. The fact that the piece is sitting in the sink, associating with unwashed cutlery, is enough to get me to move along.

A more forceful approach might backfire. If I surrendered my coffee paraphernalia to a neighbor every lunch hour, I'd quickly develop a ritual of going to a coffee shop right afterward. The velvet rope doesn't alter your path by force. It guides, suggests, implies, reminds. It leaves the choice up to you, but makes that choice slightly easier. The key is that it's still a choice-only when you're still choosing can you call it self-control.

I could choose to step over the velvet rope, by washing the container and making coffee anyway. But even then, late-afternoon coffee drinking would still be an exceptional rather than normal choice, simply because of the small, surmountable obstacle that's now in the way. When it's perfectly easy to undermine yourself, you often will. When the self-defeating act becomes a little harder than perfectly easy, you probably won't.

That's all velvet ropes need to do: make it slightly harder than perfectly easy to go the wrong way. The key is identifying that juncture in time and space where the easiest thing is the inappropriate thing, and putting some tiny, gentle obstacle in the way.

What's the thing you keep doing that you wish you didn't? Can you put something in the way?

Once you know where you tend to veer into trouble, the flow can often be interrupted by a single symbolic barrier-a rubber band around your wallet, a paperweight on top of the cookie jar, a line of tape on the gallery floor.