Here’s my Q&A column from the WSJ this week — and if you have any questions for me, you can tweet them to @danariely with the hashtag #askariely, post a comment on my Ask Ariely Facebook page, or email them to AskAriely@wsj.com.

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Dear Dan,

Apple recently announced Apple Pay, which will allow iPhone and Apple Watch users to simply wave their gadgets to pay for purchases. How might this technology change our spending habits? Could Apple Pay and other such hassle-free payment mechanisms (such as Amazon’s “1-click ordering”) lead us to spend more—particularly on stuff we don’t need?

—Nikki

The essence of payment is opportunity cost. Every time we face a purchasing decision, we should ask ourselves if getting this one thing is worth giving up the ability to purchase something else, now or in the future.

Different ways of paying make us think differently about those opportunity costs. For example, if we have $20 in cash in our pockets, we will have a hard time not thinking about opportunity cost. If we consider buying a sandwich, we realize that we won’t have money for coffee; if we get a cab, we realize that we won’t have money for dinner. But when we use a credit card or gift certificate, our thinking about opportunity cost will be less natural and prevalent—which means we’re likely to spend more without fully thinking about the consequences.

This is why the general answer to your questions is both yes and no. As you suggest, electronic payment mechanisms can easily lead us to think less about opportunity cost and spend more recklessly. But this doesn’t have to be the case. Electronic payment could be designed in ways that get us to more fully understand our opportunity costs and make more reasonable decisions. Apple Pay and the like could be game-changers, helping us think about our spending much more rigorously than we ever could with cash.

So the questions are: Who is designing these electronic wallets, and for what purpose? Will they be designed to get us to spend more money—or to help us make better decisions? Right now, electronic payments seem to be going down the path of less thinking and more spending—but I hope that at some point, some of the payment companies will change their approach, adopt the perspective of their users and offer electronic payment methods that help us make better financial decisions.

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Dear Dan,

How can I tell people who email me that I simply don’t have the time to respond to everyone?

—Kat

There is a well-known finding that when you ask couples how much each of them contributes to their relationship, the total far exceeds 100%. That is because we see all the things that we do, small and large, but we fail to see all the things that our partner does. The same is true for the people you respond to. They probably see how busy they are, but they have a hard time understanding the demands on your time.

So why don’t you create an automated email response that lists all the demands on your time, including how little time you have for sleep, exercise and your social life? With this kind of information, I hope, the people you email will understand why you can’t help them.

And while you perfect this approach, make sure you also—nicely—make your significant other aware of all the things you’re doing for the household and the relationship.

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Dear Dan,

Do people use twice as much single-ply toilet paper as double-ply?

—Gary

When toothpaste makers started putting a larger hole in the tube’s cap, people started using more toothpaste. That is because we judge the amount of toothpaste we apply largely by the stretch it covers on the toothbrush, not by its thickness or total volume. I suspect that the same principle is at work with toilet paper, which would mean that we judge the amount of toilet paper by its length—and don’t sufficiently adjust our use to take the added thickness into account.

See the original article in the Wall Street Journal here.