"Most of us have been brought up to believe we aren’t good enough and the brokenness we feel is our fault. And, if we work harder, we can fix it.
"It is extraordinary how long this goes on for and how long it persists."
When he utters them at a Mindfulness in Schools Project conference in London, hundreds of people – from students to teachers - fall still as they recognise these words from within themselves.
The conference brings together those who want to introduce mindfulness in their schools with teachers who practise it and students who have tried it.
Mindfulness – for those who are unsure – is the practice of being present in the moment.
If that sounds too vague, it means giving yourself room to take a step back from what you are doing and breathe or, as Dr Williams would say, 'to examine the weather pattern in your head'.
In doing so, you create a pocket of calm and can put aside the problems you have had in the past or worries about those you may face in the future.
In schools, which are naturally frenetic environments, advocates believe this can have a big effect on a child in terms of focus, kindness, empathy and self-understanding.
Imagine the impact it could have on bullying and the ability to self-regulate at a much younger age, they say.
In her report, 'Developing Mindfulness in Children and Young People', Katharine Weare, emeritus professor at Exeter and Southampton universities, said: "They come to see that thoughts are mental events rather than facts.
"This gradually modifies habitual mental and behavioural patterns which otherwise create and maintain negative mental states, such as rumination, stress, anxiety and depression, and makes for greater mental stability, calm, acceptance, appreciation of what is rather than hankering after what is not, and thus higher levels of happiness and wellbeing."
Perhaps the most striking change in the mindfulness world is how it is fast becoming a key addition for schools which place student mental wellbeing at the top of the agenda.
Cynics - or those choosing to place it in a 'nice if you have the time for it' box - can’t ignore the positive effect wellbeing is having in school rankings.
In January, Nicky Morgan, Secretary of State for Education, spoke at the Sunday Times Festival of Education, and challenged teachers to ask what they were doing to promote wellbeing and mental health among their students.
Amy Footman, head of school at Stanley Grove primary school, says education is finally catching up with that.
"In the new Ofsted framework there is a lot of talk about emotional and mental health," she says. "Every school has a fleet of first aiders and what (I am) hoping to do in (my) school is to prepare staff to deal with mental first aid.
"If you have mindfulness running through your culture, you are better at… reading them in a much deeper way than just listening to their words."
A couple of years ago mindfulness in schools was viewed as a nice add-on or, worse, a fad. Now, there is increasing evidence that it is helpful when used alongside other treatments for mental health problems such as depression and anxiety.
In other words, less of a handy extra and more of an essential.
Since most mental health issues in adults first emerge when they are children, could mindfulness be used – as well as other tools – to help bolster children’s coping mechanisms, how they relate to each other and, in turn, how they relate to themselves?
As emeritus professor of clinical psychology at the University of Oxford and director of the pioneering Oxford Mindfulness Centre until his retirement in 2013, Dr Williams has been at the forefront of research into its potential.
He is conducting a study called Myriad, across 76 schools and involving up to 5,000 students. It is one of the largest studies of its type.
The study focuses on 11-year-olds because, Dr Williams says, "mental health difficulties really kick in at the age of adolescence – that’s when children who perhaps have been struggling a bit but who have managed before suddenly find that they can’t manage".
He adds: "They get an adult-like problem, an adult-like anxiety or adult-like depression. Even earlier than that attention problems start and one of the things about kids is that they don’t recognise they have a problem, so they don’t seek help."
Children’s mental health – and, here, we are not just referring to illness but also mental wellbeing – is at crisis point and figuring out how we address this could be critical to prevention in adulthood.
"One of the nice things about mindfulness," Dr Williams told The Huffington Post UK, "is it’s not a treatment as such, it’s a mental skills training for the mind and we know it affects wellbeing, we know it reduces depression, but that’s a by-product.
"It’s a by-product of being able to learn with some stability, how to focus in the face of some very big external distractors – that we all have even as adults - but also internal ones such as telling yourself 'you’re stupid, that you’re no good, you don’t make friends' and so on."
Even the bean-counters should be impressed by how much money would be saved by investing in supportive, preventative services in children against the fortunes spent firefighting mental illness in adults.
Tim Loughton, MP for Shoreham and East Worthing and co-chair of the Mindfulness All-Party Parliamentary Group, said there were "good, financial imperatives for the government to act" particularly since the numbers of 16-year-olds diagnosed with depression has doubled.
His wish is that practices such as mindfulness become the mainstream, not the add-on.
Of course, mindfulness can’t 'fix' things. Teachers and practitioners are keen to point out it is intended as a support, not a replacement for other types of therapy or medicine.
Richard Burnett, co-founder of the Mindfulness in Schools Project, helped to devise .B, a highly successful mindfulness programme taught in secondary schools.
That is being followed by Paws B, which is aimed at seven- to 11-year-olds, after it was felt there wasn’t much support for primary school children.
At secondary level, this might involve 'beditation' which is a classroom of students all lying down for a short meditation session. For primary school children, they might use a 'weeble', which is a weighted toy that can wobble from side to side, which they can use to demonstrate their mood.
Although he is a passionate advocate of mindfulness, Burnett says: "Mindfulness trainers in school have to recognise the limits of it.
"If you have a child who is damaged and psychotic and suicidal – which happens, not irregularly – actually you need medication and hospital and very close clinical care.
"Mindfulness can help but it needs to be in very small groups with clinically trained professionals. Where I think it can make a massive difference is just in shifting the bell curve of wellbeing over towards the healthier end."
Nine-year-old Lauren, who speaks at the conference, and has done Paws B says: "It helps the children in my class to be calm, usually after break."
Outside the doors to the auditorium, the walls are strewn with drawings from children who have done mindfulness.
"I’ve used mindfulness to comfort me or when I’m about to hit my sister," reads one, "but I stop and think of the consequences. I’m about to shout but I stop and think."
Another child talks about how mindfulness helped her calm down before a big dance recital, and she even showed her friend how to do the right breathing and it worked for her too. One writes an affirmation: "Don’t fight fear but train the mind to adapt to it." Sometimes it takes adults years to learn how to do this – it’s pretty remarkable if a 10-year-old can grasp this.
However, experts are also keen to stress that it isn’t a panacea and it may not work with every child.
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Geography-teacher-turned-mindfulness-trainer Paula Kearney says: "I have had students who haven’t quite found it has worked for them but I also haven’t had anyone be really brutal about it and they can be about things they don’t like."
Cynicism among students is not as steep a barrier as many might think.
Una Sookun, assistant head at an inner-city London secondary school, says there is a shift in how students perceive their own emotional stability.
"An awful lot of kids are exposed to mental health problems and they are definitely interested in their own health," she says.
Amy Footman says the biggest impact is on self-awareness. A child, who might previously have had an angry outburst and then been excluded from class, is able to self-regulate much better.
She says: "We know mindfulness isn’t going to stop you having a violent outburst – and I’m clear with the children – 'this isn’t going to stop you feeling angry or sad'.
"But it might help you notice when that’s happening, and give you the space to make a choice to say: 'You know what Miss, I need five minutes. I’m not able to talk right now, but I will be'."
As for convincing parents it is a good thing, Paula Kearney finds students provide the best PR for it.
"So often it’s those who are tagged as a bit naughty or louder than the rest, who are really good advocates for how it works because they are a lot more open about how they use mindfulness and how it helps," she says.
With the tide inexorably pulling mental health alongside physical wellbeing as a priority for schools, and a crisis of adult mental health problems, it is worth reflecting on why mindfulness and self-awareness can only be a good thing in the long term.
"Studies have found kids who have difficulty with self-control often turn to be adults who have problems," says Dr Williams. "Mindfulness isn’t the control of the 'top down' – so just another instruction for children, but the sense of becoming captain of your own ship again.
"The sense of being able to pause, to check in and notice. Then to take account of your own mood before taking the next step or action. And that’s got to be good."
Young Minds Matter is a new series designed to lead the conversation with children about mental and emotional health, so youngsters feel loved, valued and understood. Launched with Her Royal Highness, The Duchess of Cambridge, as guest editor, we will discuss problems, causes and most importantly solutions to the stigma surrounding the UK’s mental health crisis among children. To blog on the site as part of Young Minds Matter email email@example.com