I don’t remember the context in which my psychoanalyst first brought to my attention how much I hate to feel disappointed. I do remember that I laughed. Who doesn’t hate it? That’s why it’s called disappointment, as Seinfeld would say.

But then I reflected on what she had said, and it really made me think.

I began to wonder why it is that disappointment is so particularly loathsome for me – even more than grief, or pain, or envy. I hate the way it makes me feel a little bit sick, as if I’m keeping it in my body so I don’t have to let it into my mind. I hate the way it makes my throat hurt, as if tears would come if I let them, but I won’t – or can’t. I hate the way I struggle even to recognise it because I am working so hard, unconsciously, to keep it at a murky distance.

But, unfortunately, I have learned through my work as a therapist, and my work as a patient in analysis, and through my experience of life, that disappointment – as detestable as it is – is absolutely vital. Counterintuitive as it sounds, I think a better life is one with more disappointment in it.

If we are too afraid of this feeling, we will remain stuck where we are, unable even to step outside the front door. It is easy to see how seeking to avoid disappointment could lead us never to try anything new, never to embark on a new relationship in case it ends badly, never to apply for a new job in case we don’t get it, never to take a risk on something we might enjoy or might not enjoy. This, of course, is the surest way to live a disappointing life. Allowing this feeling in and listening to it is crucial for learning from experience and working out what is truly important to us. I used to consciously lower my expectations so that I didn’t have to feel disappointed if something didn’t work out – but I’ve realised now that this is just another way of turning away from something that really needs to be faced.

But I think it goes even deeper than that. I think the experience of being disappointed and tolerating that feeling establishes the foundations for all mental health.

You may not like Freud’s theory of the oedipal complex; many don’t. His revolutionary conceptualisation of family dynamics – that every child feels desire for the parent of the opposite sex, and murderous rage towards the parent of the same sex (and, at the same time, desire for the parent of the same sex, and murderous rage towards the parent of the opposite sex) – is a shocking thing to contemplate, as shocking today as it was when he wrote about it in 1899.

Critics have come up with all sorts of defences against the truth of this theory, and abusers have tried to corrupt it to defend their indefensible acts. I think there is a great deal of meaning in the shape of it and, much as I would like to, I find it impossible to deny that every child, deep down, wants to have each of their parents all to themselves, and to get rid of all rivals that stand in their way. I have seen how this can play out in different dramas throughout a person’s life, and how many of our relationship difficulties echo this triangularity, from children “stealing” each other’s friends at school, to adults “stealing” each other’s partners. There’s a lot of it about.

The only healthy conclusion of this triangle is for the child to be disappointed. Every son and daughter has to come to terms with the fact that they cannot marry their mummy or their daddy, they cannot take the place of either parent, because they are a child. They might feel they want to be a grownup, might feel absolutely desperate to be elevated above their siblings, might enjoy feeling helpful or responsible – but they have a deeper need to be treated as a child, with all the disappointments that brings.

As I learned in my training, and in my own life, if a child steps into the role of an adult too early, they can end up with a sense of themselves as someone who looks like an adult on the outside, but who doesn’t feel as if they’ve really grown up on the inside.

So as I try to help my daughter to bear her disappointments in the most understanding and loving and robust way I can, I am also in a process of developing my own capacity to tolerate my version of this feeling. I can understand why she is outraged and disappointed when I tell her no – and sometimes I find myself wanting to say yes out of fear of her reaction, especially if we are in a public place – but how will she ever be brave enough to say no if I’m too afraid to? I often notice that after the tears and the comforting, she seems to feel more settled, more held than she did before. But it is hard: apart from anything else, I am trying to help her digest something that I find quite indigestible myself.

Some good friends recently told me their young son was crying and raging because, in his words, “I want everything that I want.” It’s cute when it’s a child, but I think there are many adults who still haven’t grown out of this, who rage and fight against the word “no”. The truth is, we all have our moments. One of the lessons my friends are helping their son to learn, which we all have to re-learn again and again throughout adulthood, is that sometimes – perhaps all the time – you cannot have everything that you want. It’s a very painful fact of life, and it is extremely disappointing. But, out of that rich and fertile disappointment, a better life can grow.

• Moya Sarner is an NHS psychotherapist and the author of When I Grow Up – Conversations With Adults in Search of Adulthood

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