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,

As a personal trainer, I work with older adults who say they want to exercise every day. But after a few sessions at the gym, many of them don’t come back. How can I get them to stick with their exercise program?

—Hal

There are lots of ways to make exercise into a habit, but to start with I would change the way you end your sessions—and I would try to engineer the experience so that it makes people feel good at the end. Research on the “peak-end rule” shows that when people evaluate an experience, they pay particular attention to the end.

In research published in 2016 in the Journal of Sport & Exercise Psychology, Panteleimon Ekkekakis, Zachary Zenko and I showed that when people ramp down the intensity of the exercise at the end, they feel happier after the exercise session and expect to enjoy future exercise more. So, when an experience ends on a more positive (or at least a less negative) note, we remember the whole as better and are more likely to want to repeat it.

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Dear Dan,

I’ve wanted to buy a new iPhone for a while, and I’ve been holding off so that I can save for a vacation with my wife. But recently, I got some extra money as an end-of-the-year gift from my job. I’m tempted to use this money for my vacation and the money I have been saving in the bank toward a new phone. Why am I thinking differently about spending the gift money versus what’s in my savings account?

—Ron 

An essential feature of money is that it’s fungible: this means that each dollar is in principle worth the same. Yet, in reality, our minds create separate “accounts” for different sources of income and expenses, and we spend money based on what we think is reasonable for each account. Behavioral economists call this “mental accounting.” When you got some extra end-of-year money, it felt like this money belonged to a different account from our standard savings.

This is clearly not an ideal way to think about spending. I would put the year-end money in your saving account for a month or two, let the money “get used” to its new mental account (more accurately to let you get used to it), and only then decide what to do with it. My guess is that in two months you will feel less inclined to splurge on the phone.

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Dear Dan,

What are the odds that my New Year’s resolution to eat healthily every day will stay with me until the summer?

—Yoram 

Very close to zero. If I were you and I wanted to increase the odds of success, I would make the resolution more clear-cut, and I would allow myself a way to eat less healthily from time to time without feeling like I’ve failed. For example, to make your resolution more specific, replace “eating healthily” with cutting out baked goods (for maximum effect, be specific and include both breads and sweets). And to give you a way to enjoy life without feeling like a failure, take the sabbath as a day off from your diet.

See the original article in the Wall Street Journal here.