I was in my mid-20s and living in a house I shared with some old friends and new mice. One night, I was waffling on about something trivial, but giving it great weight. My best friend, Jules, looked at me with pity and disdain and said: “Lou, I can’t bear to be around you, you’re just so negative.”

Best thing she ever said! The finality, the rawness, the reality – she saved me from my own silly self. I didn’t know it at the time, of course – too negative to see it, I suppose.

Like a lot of kids, when I was really young, I was overjoyed with life. Dancing, prancing and mucking about. Shoving Lego up my bum with a smile on my face. Five-year-olds have the right idea (not so much about the Lego; that’s a waste of a good toy). But young kids have life sorted. Not a lot holds them back. You want a song? They will sing it. You want someone to live in the moment? They’re on it – although they can’t tell the time.

I was relentlessly positive. I was enchanted by life and very grateful. I had watched enough Blue Peter appeals to know that running water was a luxury, thank you, and I was more than happy to explain this to everyone I knew. I would jump around exclaiming: “We’re so lucky – looky here – water out of the tap! They haven’t got that in Africa.” Yes, sure, colonially patronising and geographically ignorant, but it was a different time.

I would leave loving thank-you letters for my mum, brother, stepdad and cat – and the last three in that mix didn’t even particularly like me at the time – but looking back now I can sort of see why. I had the persona of a Californian divorcee who has rebuilt their life and runs a course called “An attitude of gratitude with a side of sass”.

But, bit by bit, life chips away at you. It happens to most people: you are told it’s not just a game, you take on responsibility, you weather knockbacks, you are told ice-cream is not a meal. You grow up and get real. Life, it turns out, is not what you thought it would be.

By the time I was 25, I was a full-on neg head – and not in a funny way, either. I have friends who bemoan everything and it is hilarious: they’re great value – they are funny! The difference is they’re not looking to others to fix them, they are not sucking people’s energy. In fact, they get a twisted pleasure from deriding everything and the way they do it is paradoxically joyous, because they are having fun.

But true vibe-killers, like I was – there is nothing funny about them. And they make life harder for themselves, because, to some degree, you get what you expect. This has been proved by social scientists such as Richard Wiseman and social idiots like my friend Unlucky Barry.

When I was 25, it was not like I was in a war zone or a hospice. I had a colourful backstory, but lots of people had it way worse. The main thing in my way was my own goddamn attitude. So Jules’s wake-up call was a gift. It forced me to get positive. This did not happen overnight, but – bit by bit, month by month, year by year – I did it. I devoured self-improvement books, I watched Eckhart Tolle on YouTube, I observed other people and questioned how they approached life. I was committed to resetting myself to be more joyful and, as I became better at it, my life became better.

Is this true, or did I just view my life more optimistically? Who cares – the result is the same. Externally, things did improve and I was more fun to be around. I know some people will roll their eyes at this – it sounds so millennial, so navel-gazing, so self-obsessed and privileged. Maybe, given the state of the world now, it seems fluffy, light, insidious and irresponsible even to see some of the suffering and say: “Smile, it’ll be all right!” But that is not what I am saying – lots of things won’t be all right and lots of things will. That’s why you have to enjoy the good bits and not wait for the bad. When the sun is shining, enjoy the sun; when the rain is raining, dance in the rain – you’re going to get wet anyway. And if you slip and injure your back, at least you get some time to relax in hospital.

Lou Sanders: Shame Pig is touring from 16 February

• Read more stories of change in the G2 special issue A new start on 31 December