A year ago I argued that societies can benefit from settling on a particular date on which people commit to making changes in characteristics—such as kindness, forgiveness, and tolerance—that affect interpersonal relations. The consequences of this may even be strong enough to detect in data, although December and January differ in so many other ways that causal identification would be challenging.
What is true for societies writ large is also true for smaller components, but with an interesting twist. Synchronized resolutions can affect interactions in ways that cause some friendships to deepen while others fray.
Imagine a group of friends who meet pairwise from time to time for a meal or a walk or some other social activity. The pleasantness of these interactions will depend, of course, on the manner in which each party behaves.
Now suppose that some members of this group decide, in an entirely private manner, to make changes in their behavior. For example they may decide that they will be more punctual to appointments, or less obstreperous during them, or that they will silence their phones in the company of others. This will change the nature of all their interactions. But the changes will be especially stark and enduring in encounters with people who have (privately) made the same kinds of pledges.
Notice the role of synchronization here. If I resolve to be more punctual while the person I’m meeting does not, I’ll just end up waiting longer than I otherwise would. I’ll bear an additional burden for no discernible benefit, other than the satisfaction of having kept my word to myself. This may be enough to keep me going for a while, but my resolution is quite likely to be abandoned before long.
But if both parties make the resolution simultaneously, they will each experience material benefits right away. Interactions will start sooner and may extend longer. They may be repeated more often than they otherwise would. And even if interactions with everyone in the group were equally valued in the past, some pairwise encounters will start to be valued more in the future. A few people will move closer together while others drift apart.
I hope that the new year will be a happy one for everyone reading this, but I suspect that it will be especially happy for those who resolve to make others a little happier. Provided, of course, that they are fortunate enough to have people within their circles who are making the same kinds of resolutions at about the same time.

Great article, and I think you capture one side very clearly: there can be a lot of benefits to synchronized resolutions. But, there can also be costs: some resolutions may be easier to keep if people were not all doing it at once (e.g., would people be more likely to stay with the gym if they started at a random time of the year or when a lot of new people are showing up?), and some resolutions may be more prevalent if our resolution day was in a different time of the year (e.g., are some healthy ideas like daily walks undermined by resolutions starting in January?). There could be a very interesting model about what types of resolutions benefit from coordination and what does not.