Notes
This book gives general information. It isn't medical or psychological advice, and it's no substitute for a doctor or therapist who knows your situation.
I've kept sources out of the chapters where I could so they read easily. Here they are by chapter, with the limits I'm aware of. Unless I say otherwise, I read the published summary of each paper and not the full text. I checked each paper for a retraction notice in September 2026 and found none. Where a chapter isn't listed, it rests on my own reasoning. That includes chapters 1, 2, 5, 6 and 15, the message in chapter 12 and the rule in chapter 13. The NHS pages were read in September 2026. They're written for England or the UK, and services differ elsewhere. Most of the research was done in North America and the UK, much of it with students or online volunteers, and much of it concerns strangers or brief contacts. Carrying it over to long-standing friendships is my step throughout.
Before you start. The two-week threshold and the routes to help are from the NHS page "Get help with loneliness". The remarks on social anxiety are from the NHS page "Social anxiety (social phobia)".
Chapter 3. Aknin and Sandstrom, "People are surprisingly hesitant to reach out to old friends", Communications Psychology 2, 2024, article 34. I read the full text. Seven studies with 2,458 participants in total. In studies 3 and 4 fewer than a third of participants sent a message. In study 5, 288 people rated their willingness to do eight everyday activities. Contacting an old friend and talking to a stranger both averaged 4.6 on a seven-point scale. The authors report that willingness to contact an old friend was lower than for all but two of the other activities, those two being booking a medical appointment and sorting a bag of coins, and that not all the differences were statistically significant.
Chapter 4. Liu, Rim, Min and Min, "The surprise of reaching out: appreciated more than we think", Journal of Personality and Social Psychology 124, 2023, pages 754 to 771. Epley and Schroeder, "Mistakenly seeking solitude", Journal of Experimental Psychology: General 143, 2014, pages 1980 to 1999. The commuters were in the Chicago area, and I haven't looked into how well the finding has held up elsewhere.
Chapter 7. Boothby, Cooney, Sandstrom and Clark, "The liking gap in conversations: do people like us more than we think?", Psychological Science 29, 2018, pages 1742 to 1756. The studies concern people getting acquainted, not established friends.
Chapter 8. Cacioppo and Hawkley, "Perceived social isolation and cognition", Trends in Cognitive Sciences 13, 2009, pages 447 to 454. Hawkley and Cacioppo, "Loneliness matters: a theoretical and empirical review of consequences and mechanisms", Annals of Behavioral Medicine 40, 2010, pages 218 to 227. Both are reviews by the same research group. Masi, Chen, Hawkley and Cacioppo, "A meta-analysis of interventions to reduce loneliness", Personality and Social Psychology Review 15, 2011, pages 219 to 266. The authors note that the less rigorous studies showed larger effects than the randomised ones. Holt-Lunstad, Smith, Baker, Harris and Stephenson, "Loneliness and social isolation as risk factors for mortality: a meta-analytic review", Perspectives on Psychological Science 10, 2015, pages 227 to 237. The odds ratios were 1.29 for social isolation, 1.26 for loneliness and 1.32 for living alone. The likeness to a habit that relieves a discomfort it builds is my interpretation.
Chapter 9. The distinction between being alone and being lonely is from Hawkley and Cacioppo 2010. The check by the pang is mine.
Chapter 10. Sandstrom and Dunn, "Social interactions and well-being: the surprising power of weak ties", Personality and Social Psychology Bulletin 40, 2014, pages 910 to 922. Hall, "How many hours does it take to make a friend?", Journal of Social and Personal Relationships 36, 2019, pages 1278 to 1296. Two studies, with 355 adults who had recently moved and 112 first-year students. Both papers report associations and can't show cause.
Chapter 11. Kumar and Epley, "It's surprisingly nice to hear you: misunderstanding the impact of communication media can lead to suboptimal choices of how to connect with others", Journal of Experimental Psychology: General 150, 2021, pages 595 to 607. What I say about watching friends on social media as a substitute for contact is my view and I haven't looked for research on it.
Chapter 12. Kardas, Kumar and Epley, "Overly shallow? Miscalibrated expectations create a barrier to deeper conversation", Journal of Personality and Social Psychology 122, 2022, pages 367 to 398. Most of the experiments paired strangers. Predictions were more accurate for conversations with close friends, family and partners.
Chapter 13. The practice study is study 7 in Aknin and Sandstrom 2024. There were 194 participants, recruited on a university campus in the UK. Those in the practice group sent messages to about three current friends or acquaintances on average. Plans in "when, then" form are from Gollwitzer and Sheeran, "Implementation intentions and goal achievement: a meta-analysis of effects and processes", Advances in Experimental Social Psychology 38, 2006, pages 69 to 119. The rule and its four parts haven't been tested together, and what I say to expect is my expectation and not a finding.
Chapter 14. The suggestions about groups, volunteering and social prescribing, and the advice on when to seek help, are from the NHS page "Get help with loneliness". The rule of two is mine.