“Death, like the sun, cannot can be looked at steadily,” La Rochefoucauld wrote in 1678 – a line that sounds modern because what it describes is as true as ever. This is a book to make time for precisely because it faces a subject most of us shy away from. Julia Samuel is a grief psychotherapist who has spent 25 years working in the NHS at St Mary’s hospital, Paddington, and in private practice. She suggests not only that death is hard to contemplate but that we are discomfited by the idea of grief, encouraged to put a good face on loss and hasten towards “a new normal” (ghastly phrase). Samuel writes: “Death is the great exposer: it forces hidden fault lines and submerged secrets into the open.” Grief, she believes, is “profoundly misunderstood”.

Unresolved grief has been found to be at the root of 15% of psychiatric referrals but, as Samuel makes clear, resolution is not always straightforward or even possible. She does not – hurrah! – believe in “closure”. Nor does she feel denial is always unhelpful. She is non-prescriptive, open-minded and admits to her vulnerabilities. What is marvellous is Samuel’s ability to feel for – and with – her patients. She emphasises that friends should never underestimate the importance of sympathy. Being a good listener is “by no means the sole preserve of professional therapists” – and listening is vital. It should be added that, should a suitable friend be wanting, Samuel would make a great substitute.

Paradoxically, it is the insistence on writing about what cannot be fixed that is the most powerful thought in a book that has a real chance of helping bereft readers: “Our culture is imbued with the belief that we can fix just about anything and make it better; or, if we can’t, that it’s possible to trash what you have and start all over again. Grief is the antithesis of this belief: it eschews avoidance and requires endurance, and forces us to accept that there are some things in this world that simply cannot be fixed.” The book is filled with case histories written with the permission of the people described. They are fascinating, affecting, but often not easy to read: there were points where I wanted to run away, especially from the accounts of parents who have lost children. (I recognise this to be a reflex similar to the shameful impulse that makes some people cross to the other side of the street rather than face a recently bereaved parent.)

Grief Works considers the deaths of partners, parents, siblings and children. There is a chapter on suicide, another on facing death ourselves. Samuel ventures to hope we might “be surprised to see much of ourselves in someone who is grieving an entirely different death”. And we do – although she is sensitive, too, to the thought that each person grieves differently. Even within a family, grief is seldom uncomplicatedly collective. The book’s aim is to serve as a resource, a way of understanding grief better and “living with a reality that we don’t want to be true”.

Samuel also writes about the unspeakable yet understandable emotions sometimes present when a person is dying – such as a terminally ill person’s jealousy of the living. In one case history, Brigitte, who lost her mother, confesses to feeling jealous of her daughter for having what she herself now lacks: a living mother. Brigitte is a case history for our times. Grief must not be hurried yet Brigitte’s outward behaviour suggests she has no time in which to mourn: “There is an epidemic of busyness in our world today, and Brigitte displayed a full-on version of it. Her smartphone, which was hermetically sealed to her hand, perfectly embodied the false idea that busyness is potency.”

When Kaleigh’s partner dies in a road accident, she stops eating, binge drinks, feels suicidal. She uses her phone to motivate herself with the wallpaper message: JFDI (Just Fucking Do It). Only that, often, she doesn’t. Samuel struggles to maintain her own equilibrium: “Kaleigh’s turbulence had become contagious: I felt shaken up.” The book is full of Samuel’s responses – possibly breaking a therapeutic rule – but I found these refreshing, a way of making encounters two-sided, a reminder that you do not have to be a friend to be affected by another person’s suffering.

Samuel is as observant as a novelist but responsible about what she describes. She describes Stephen’s talking “in the third person, like an observer looking at someone he knew”. The book is full of acute perceptions and surprising statistics: 4,400 people in England kill themselves each year, one every two hours… Men tend to start new relationships within a year of their partner’s death… A bereaved person is six times more likely to suffer heart disease than the national average.

I was moved by the portrait of “Caitlin”, an exuberant Irishwoman, whose husband, a recovering alcoholic, was dying of liver cancer. Samuel makes sure you never forget that death happens in life – and that life is messily ongoing. She reminds us that grief is not an illness and can, for some people, eventually be a spur. “Pain is the agent of change,” she writes – and that change is sometimes positive for survivors. She points out that death ends a life but not a relationship. She has practical suggestions – uncontroversial but boosting – for getting through the hardest months (talking, exercising, writing). She compares Caitlin, in her gradual emergence from grief, as resembling a mosaic in a Roman villa with some scuffed or cracked tiles and others that are untouched and “show a perfect picture”. It is a well-chosen image because she never pretends it is possible to restore the mosaic completely.

It is inevitable that, in the course of reading this book, one starts to wonder (as patients will about their therapists) about Julia Samuel herself. What can it be like for her to spend so much time in the shadow of death? It turns out she was born into the Guinness family, was a friend of Princess Diana’s and is godmother to Prince George – but these connections are not included in the publication details out of fear, presumably, of too much distracting royal icing. All the same, there is a missed opportunity here: it would have been fascinating to know what Samuel thought about the national outpouring of grief (if that is what it was) after Diana’s death. It would have contributed to her outstanding and indispensable survey of the subject.

• Grief Works by Julia Samuel is published by Penguin Life (£14.99). To order a copy for £11.24 go to bookshop.theguardian.com or call 0330 333 6846. Free UK p&p over £10, online orders only. Phone orders min p&p of £1.99