It’s almost a year since my dad died. Even though he lived , and even though his health problems began when I was a child, his death was nevertheless a terrible shock. It still is. It was the most predictable thing in the world, but I still can’t believe it. The wave of grief surges up whenever I think of a joke he would have liked, or whenever I hear his advice in my head, and whenever I catch sight of his ashes, stored in a Hellmann’s mayonnaise jar on my bookshelf until a more suitable container can be found. (He liked Hellmann’s, but not that much.) Each time I’m left gasping for air from the pain and, strange as it sounds, I’m grateful for it. Because I know this grieving life is far better than the alternative.

Years ago I volunteered as a bereavement counsellor, and I remember vividly the moment in training where it finally clicked: my job was not to take away people’s grief, but to help them feel it. You see, you may not need counselling or therapy if you are truly grieving; but you may well need it if you aren’t. Grief is a horror, and it’s supposed to be. Where grief has got stuck, or when it has still not even begun – that is when you might need a protected space, and time, and a good, receptive listener with whom you can find it in yourself to truly suffer the pain of your loss.

As a psychodynamic psychotherapist, I have learned that the capacity to feel loss and grief constitutes nothing less than the foundation of all mental health, from infancy through to old age. Whatever life stage we are in, the inability to experience loss and to mourn it means we remain fixed where we are, unable to develop, desperately trying to hold on to whoever or whatever it is that is gone. It might be a person, a relationship or a dream that has died, but if we scroll or drug or literally run away from our feelings, the result is the same: we’re trapped. Without loss, without grief, there can be no growth.

It was kind of funny – not to mention reassuring – after learning this for years in psychotherapy training, to then be told exactly the same thing when I began researching my book about adulthood. When I asked people when they knew they had grown up, many spoke about losing someone they loved, and having to find the resources inside themselves to face up to that loss and to feel all the feelings that came with it. They felt, eventually, that this experience brought meaning to their lives and propelled their development in some way.

Like Sara, who described how she always felt that she didn’t know what to do in certain situations, and needed to ask others for their advice – until she lost and mourned her mother. She now feels she can overcome any problem and find the solution within herself. “When my mother died, I had to walk through fire and survive that loss, carry on and grow up out of that grief, and into the truest version of myself,” she said.

Others recognised they had not yet been able to grieve, and that this had a cost. Sam, who lost his mother at 13, described only crying on the day of the funeral, and never allowing himself to cry again. “I think it’s a very problematic thing,” he said. “For a while, I was like: yeah, that’s great – I’m not in pain. But now I’m clearly struggling to feel at all. I feel like tears should be able to come out of these eyes, but they’re not.”

At first, as I busied around working through the sadmin that follows a death, writing my dad’s eulogy and choosing bagel fillings for the funeral guests, I didn’t feel any pain at all. I was so preoccupied with trying to hold everything together, I lost touch with my own need to fall apart. I felt completely disconnected from myself and my dad – as if I was half in and half out of my life. Everything was blurry, because I couldn’t bear to allow myself the clarity of my grief. I knew then that this state was far worse than feeling the loss, but I also knew I couldn’t make myself feel something I wasn’t ready to feel. Looking back now, I think I was probably frightened of all the emotions to come. And I was right to be. But I knew I had to face them eventually, because that undead, colourless half-life lies ahead if we cannot find the courage to give ourselves the cacophonous gift of grief.

So I am grateful for my grief, and all the pain and anger that comes with it. Because I know that for me, this way lies the better life. It may not be easier, but it is real and true, and it is mine.

• Moya Sarner is an NHS psychotherapist and author of When I Grow Up (Scribe Publications, £10.99). To support the Guardian and Observer, order your copy at . Delivery charges may apply.