I didn't finish Chip and Dan Heath's 'Switch' because it was a book that should have been an essay and seemed to contain too many generalisations to my liking.
That said, I loved the popcorn study, where they filled some popcorn tubs with really stale crap popcorn, all in tubs too big for folks to finish, but some still much bigger than others.
Even with crap popcorn, the folks with bigger tubs ate much more.
Conclusion one - if you want to eat less, dont just reduce portion size, reduce the size of what it comes in (a half pint of beer in a pub gets drunk slower in a pint glass than in half pint glass).
Conclusion two - in many cases, you can't solve people problems, so look for situation problems. Instead of asking 'how do I get people to eat less' (really hard) ask 'how do I get their food served in smaller plates and bowls -easier.
Just like getting people to stop littering is really hard, but giving people a target to AIM their litter at really easy - and reduces litter because we can't resist that target.
All marketing is supposed to be about people, what they are doing, what they care about. You would be amazed how many don't think they have a people problem, they have a brand problem, or an awareness problem.
But actually, maybe a 'people problem' isn't the right way to look at things either.
Perhaps one should looks for a situation one can affect.
Many moons ago, I was tasked tby a retailer to get people interested in buying a new bed, which is of course very, very hard.
But we found that there was a much easier situation to solve. There were plenty of people who knew they needed a new bed, but couldn't be bothered with the hassle of getting rid of the old one. So put it off .
All we did was change the situation by promising people in the market (no one was doing this at the time) we would get rid of their old bed for free. Because we all choose the path of least resistance.
Then another time, we realised people were LEAVING the store because they didn't know how to choose a bed, and hated talking to staff. So we created a free guide to buying beds so they didn't have to, and made them feel like they had the upper hand when eventually a conversation had to happen.
Put another way, choose a fight you can win. Not always sexy, but very effective.