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,

I have a farm where people come to pick blueberries, and I charge $3 per pound. The problem is that people think it is an open buffet and eat a lot of blueberries while in the field, and then they come back to the payment station with just $3 worth of blueberries. Without being rude, how can I let them know that they are stealing?

—Michelle 

I must admit that when I’ve picked blueberries I too ate a few in the process. It’s just so tempting that I think it’s inhuman to ask people not to eat any. So if we accept that people will eat some blueberries in the process of picking, maybe the best approach is to charge an entrance fee to cover the cost of the snacking. But make sure to call it an entrance fee and not a snacking fee—otherwise people will try to maximize their benefit by eating even more blueberries.

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Dear Dan,

Conventional wisdom says that when providing criticism, you should use a “compliment sandwich,” that is, say something nice, give the critique and then end with something nice again. Have there been any studies regarding the effectiveness of this practice? It seems to me that the person may just hear and remember the positive parts, and that the impact of the criticism would be lost.

—Andrew 

“Compliment sandwiches” certainly feel less painful than sheer critiques—but they don’t seem to be particularly effective. According to a study by Jay Parkes, Sara Abercrombie and Teresita McCarty, published in 2013 in the journal Advances in Health Sciences Education, people who received “compliment sandwiches” were more likely to believe that the feedback would improve their performance. But they didn’t actually do any better than those who received more straightforward criticism. The good news is that the sandwich method did not get them to perform any worse either—it just made no difference. It is really hard to change people’s behavior, and a single piece of feedback is not going to do much, no matter how it is phrased.

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Dear Dan,

I teach computer science 101, and I’ve recently started thinking of ways to get students to begin their work earlier in the semester. Research has shown that if they start earlier, they are likely to put more time into their project and get a better grade. I wonder if it would be useful to send a daily email reminder asking the students to start working on their project today. What do you think?

—Kristin 

A daily reminder is a good start, and it should certainly help the students to get going. But it would be even more powerful to give concrete instructions and make use of social comparison. What if the email didn’t just ask them to work on their project today but specifically told them to spend 30 minutes on it? You could also tell them something about the work habits of students who do well in the class—for example, “Historically, the students who got an A in this class started working on their projects early and worked on them consistently throughout the semester.”

See the original article in the Wall Street Journal.