“70% off — today only — last three in stock!”

You probably had no idea that you were desperate to buy a handheld, gold-plated, three-cylinder leaf blower — plus tortoiseshell trim and personalized engraving. Not until that helpful email gate-crashed your inbox.

But then you imagine that leaf blower resolutely sending those rotten leaves on their way. How could you say no? Nibbling your nails to the quick, you hit the PayPal icon.

“Buy now while stocks last!” is a mighty sales gambit because it employs the most ancient tool of persuasion and desire: scarcity.

“Simply put, people want more of those things they can have less of,” explains Robert Cialdini, author of Influence. For this reason, compliance practitioners across the worlds of politics and retail routinely set about enhancing the market appeal of whatever goods they’re peddling by making the supply, and the window of opportunity for seizing a piece of it, appear both slender and finite.

Scarcity leaves you liable to act impulsively and less mindful of your future interests.

How does time pressure charge a dull object with glamour? Convincing you that time is short sets off an emotional tripwire, injecting spurious urgency into a mundane consumer choice. Suddenly it has the character of a drama, with you as the leading actor. The manipulative marketer hopes that part of you will feel not unlike Indiana Jones, watching that gate descend at the entrance to the tunnel, threatening to separate you forever from your lucky hat (or leaf blower). How could you not reach out and grab it?

When time itself is limited, the logical response is to use it more prudently. As it turns out, time pressure seldom makes better judges of us. On the contrary, as illustrated, it usually causes us to act less rationally.

The reason we buy and do silly things when we feel rushed is that a scarcity mentality overtakes us, drenching us in stress. In their provocative book, Scarcity, Harvard economist Sendhil Maullainathan and Princeton psychologist Eldar Shafir explore poverty and procrastination to show how scarcity is the cognitive equivalent of a poverty trap. Any form of scarcity has the same effect: No matter what resource you lack — biscuits, cash, sun loungers around a hotel pool — the stress caused will “capture the mind,” imposing a cognitive “bandwidth tax.” For instance, one study asked people with little money to contemplate a hypothetical $1,500 car repair. Their subsequent performance on an IQ test plummeted 13 to 14 points — equivalent to the mental impairment of one sleepless night. Richer people showed no such damage.

Scarcity leaves you liable to act impulsively and less mindful of your future interests. Long-term scarcity impairs your thinking in the longer term, too. According to neurological scans, sustained stress damages the brain area devoted to goal-focused decisions and actions. Worse still, it enhances the part in charge of forming habits. This is because when we feel overloaded, we release dopamine, epinephrine, and noradrenaline: neurotransmitters that encourage rash, addictive behavior.

“Thus, the part of the brain that enables creative problem solving becomes less available the more we need it,” wrote behavioral psychologist Walter Mischel, an expert in self-control.

In some cases, time pressure can be handy. There’s truth to the cliché that if you want a job done, give it to a busy person. When working to a strict deadline, your intellectual horizon narrows, driving you into what psychologists call a cognitive tunnel, but this concentrates your attention and, like Indiana Jones, you won’t rest until it’s done, zoning in on only what is absolutely necessary.

The drawback is that, inside a cognitive tunnel, you lose perspective. You’ll be “less insightful, less forward-thinking, less controlled,” as Maullainathan and Shafir put it. From a neurological perspective, you’re in a fight-or-flight state, in which you will tend to grab the nearest resource that looks like an answer to your problem.

Get in the habit of feeling chronically short of time and the price can be high. A 2008 survey found that only 6 percent of respondents who identified as busy cut back on work, while 57 percent cut back on hobbies and 30 percent reduced family time — those irreplaceable things that restore us and make time feel full.

If time is scarce, the onus is on you to be discerning about how you use it and override that scarcity mentality.

Plan your schedule when you’re relaxed and you’ll make better choices, in your own good time. Track how much time you invest in hobbies, family, and friends versus work. When during the week do you routinely face difficult choices? Assess them (in a nonpressured moment, perhaps over the weekend). If the cumulative pattern worries you, experiment. What happens if you leave the office on time for a week or spend longer over a family breakfast? Are you more or less effective?

Be alert to artificial time pressures: Why is there a deadline? Serving whose convenience? Is it authentic? If that retailer’s discount code expires at midnight, what are the chances they won’t email a new one next week?

Create an environment in which it’s easier to recognize that you’ve entered a cognitive tunnel. Record how much time bleeds on diversions or dealing with emergencies. How many distractions are exacerbated by unnecessary rushing — leading you to give them undue weight at an inconvenient moment?

Attend to when time pressure works, when it gets to be too much, and you might start enjoying it. If nothing else, build your tolerance for time pressure and it will be less stressful — making it harder for others to drive you into cognitive tunnels.

Excerpted from Enjoy Time: Stop Rushing. Get More Done., by Catherine Blyth, published by the Quarto Group. All rights reserved.