According to The British Stammering Association, 8% of children will stammer at some point, but most will go on to talk fluently. However, for up to 3% of adults, it will be a lifelong condition.
Ed Sheeran, Bruce Willis, Tiger Woods, Julia Roberts, Samuel L Jackson and US President Joe Biden are just a few famous people who stammer.
Despite this, there is very little understanding of the condition among non-stammerers and little support for young people who stammer.
"In school, I used to think that if I didn't stammer, I could be prime minister," says firefighter Peter Bradley. "I thought it was the cause of all my problems and imagined all the things I could do if only I wasn't a stammerer.
"Many people think that it's a nervous thing (I thought that myself as a child), but it's not. It's a neuro-developmental condition that can sometimes be hereditary.
"I started to stammer when I was around seven," adds Peter, 32, who lives in Carryduff with wife Lisa and baby son, Finn.
"My brother stammered in school and my dad stammered until he was in his early 20s, and I've got lots of cousins and relatives on my dad's side that would have stammered in school and beyond. They had speech therapy and that worked for them, but it didn't for me."
In October 2019, Peter was interviewed on television, talking about stammering and working as a firefighter.
"Shortly after, a young guy visited me in the fire station with his mum," he recalls. "He had never met anyone before who stammered and told me that before seeing me on TV, he never thought that he could become a firefighter. He said that it would be great if he could meet other young people who stammer so that he wouldn't feel so isolated.
"Around the same time, Jamie got in touch and we decided to co-found the Belfast Stammer Support group.
"During my schooldays, apart from my family, I didn't know anyone else who stammered and for me personally, engaging with other people who stammer has been the best therapy."
Peter agrees that school can be a very traumatic experience for children who stammer.
"In class, when we had to read out passages and things like that, I just couldn't do it. I used to wish that I could trade in my voice for a Stephen Hawking-type computerised voice box implantation to communicate for me.
"Teachers have a big part to play when it comes to acceptance of stammering," says Peter.
"When Covid restrictions are lifted, Jamie and I will be facilitating workshops with Stranmillis College to make student teachers aware of stammering, what it is and how it can affect children.
"Also the practical measures they can take to help nurture and support children who stammer and develop their confidence.
"The perception that because you struggle with vocal communication you are less intelligent, can cause a child to really doubt themselves and their self-worth.
"When I was young, I never thought that I could be a firefighter. I thought I'd be working in an office or in a position where you didn't have to speak."
Despite feeling like this, Peter finished school and went on to university. Having always wanted to work in the emergency services, he loves working as a firefighter and is very grateful to his employers for funding his attendance at the Starfish Project - a private, non-profit, adult speech therapy course in Eastbourne.
"You are taught different techniques to help and the big thing for me was dealing with issues under the surface such as lack of confidence and the opinions of others," he says.
"Support is unique to each person. Starfish helped me, yoga might help someone else. A major aim of Belfast Stammer Support is to raise funds to help young people access whatever support mechanism works for them."
Peter insists that stammering should not be a barrier to career or personal success.
"We've seen with Joe Biden that people who stammer make great leaders. My stammer has made me into an empathetic person, a good listener and a more compassionate person. Just because you are a stammerer it doesn't make you a poor communicator.
"I think it's made me a better communicator."
Support group co-founder Jamie Wilson (32) began to stammer from around the age of four.
"It was quite significant well into adolescence and it had a terrible effect on my confidence," says the physiotherapist who lives in Bangor with wife Miriam.
"I actually became apologetic for having a stammer.
"At school things such as not being able to answer a teacher when they asked you a question, I found made them assume you were an idiot.
"And because I wasn't answering, but my written work was good, sometimes teachers thought that I had copied things from other pupils.
"All the way through childhood, I couldn't ask for a bus ticket to where I wanted to go, I had to pick a destination beyond or before that I could say.
"I also had to learn how to like foods that I could say rather than ones I liked.
"I tried traditional speech therapy when I was younger, but it didn't help."
Despite his experiences, Jamie was determined that his stammer would not hold him back and after grammar school went on to university and a post-grad.
"My parents were very supportive," he says. "I was also very stubborn," he laughs. "I know I could very easily have gone the other way - gone into myself and given up on education.
"However, there are a lot of children who maybe don't come from stable homes who are struggling and if they can't put their hand up in school and ask a question, this can have a huge impact on their life and education.
"A lot of people who stammer don't achieve their full potential."
Jamie studied physiotherapy, a course and a career that requires a lot of verbal communication, wasn't that daunting?
"It was when I was a student that I started to learn about stammering, accept my stammer and start to investigate and find my own way to manage it," he says.
"I actually think that speaking to people regularly has helped my stammer more than anything else.
"I know that stammering can seem very trivial, but despite Joe Biden becoming America's President and films such as The King's Speech, nothing has really changed for stammerers.
"These days it's abhorrent to laugh at a disability, but cartoon and comedy characters still stammer to make you laugh, or stammering is used as a flippant description - a stuttering finish for example.
"Why is it okay to laugh at stammering?"
Jamie hopes that the Belfast Stammer Support group will help change attitudes and also encourage confidence and pride in young people who stammer.
"Acceptance is important - accepting that you stammer and not apologising for it is vital," says Jamie.
"We want to get kids to realise their strengths and work on their strengths, because whilst in utopian society they might be able to argue that speech shouldn't matter, in reality, it does.
"Your stammer should not hold you back but it very easily can do."
For info about Belfast Stammer Support, email: firstname.lastname@example.org; Twitter: @BelfastSupport. Information on stammering and a helpline service is available from The British Stammering Association. Go to: www.stamma.org
Stammering is statistically more common among males than females and affects men four times more than it affects women.
Dr Anna O'Brien (27) from Belfast works at Altnagelvin Hospital in Londonderry.
"I've always stammered, but more so when I went to secondary school," she says.
"I wouldn't say I had a hard time at school. I think for me, the stress came from not understanding what stammering was. And like a lot of young people, I thought it was my fault, or I was doing something wrong.
"Someone would say, 'Slow down, or take your time' and I would think to myself, 'If only I could relax, I wouldn't stammer'.
"When you're young, if you don't know anyone else who stammers, it can be very distressing and isolating. Many people try to hide it and in my experience, this can sometimes make it worse.
"My parents and family were very supportive in getting me speech therapy, but also didn't force me to do anything I didn't want to do. My school teachers and university tutors were also very supportive."
Working as a doctor, where verbal communication is key, must be difficult at times?
"It definitely was during my first year," admits Anna.
"It's a baptism of fire starting any new job and then worrying about your speech on top of that.
"But the majority of people I come across are understanding. You do get the odd person who laughs, or an offhand remark if you are struggling to say your name and things like that.
"However, when you explain that you have a stammer, the majority of the time, people are very understanding.
"That's why raising awareness is so important. People who stammer naturally listen more than they speak.
"And in a way it's helped me better understand people who have similar problems and disabilities.
"I'll always have a stammer, but you can't let it hold you back from doing what you want to do in life."