I was born with a condition called talipeses, known as club foot, so both of my feet were fused facing backwards. I underwent several procedures as a child to help reset the alignment of my feet - needless to say, a career in sport didn't seem to be what I was destined for.
But that's where I ended up: I was on the British karate team for six years, where I met a physio working with Paralympians and she explained that my foot could classify me for Paralympic sports.
I tried a rowing machine for the first time in my life when I went to a Paralympic Potential Day in 2009. A few weeks later, I'd moved to Caversham - HQ of the GB Rowing Team - and I was rowing.
I was never driven by winning medals - it was just about being out and seeing what my body could do. I love when you push to the limit and you can't go anymore and your mind's telling you, "That's it, there's nothing left," and you just find that extra 1%. I think the reward from that is an amazing feeling.
In 2009, my teammates and I took gold at the World Rowing Championships, but after that, it started to look like something had gone wrong. My performance levels were dropping. I was feeling faint and almost blacked out a couple of times.
I went for some MRI scans and they confirmed the worst: doctors had found a tumour in my spine.
Without mental resilience, I don't think I would have survived the ordeal. Going into surgery, it was very important for me to have a goal post-surgery.
If I'd have gone into those surgeries with no direction or goal, it would have been very easy to give up. It's a very daunting feeling that the last thing you might ever see is someone you don't know injecting you with an anesthetic.
How do I get through it? I imagine the tumour as an opponent who's basically trying to kill me. If I approach it like a fight, then I've got the best chance of defeating it.
All those years of doing martial arts and training my mind to fight without fear are also helping me. The thinking is that if I'm mentally strong and approach it like a fight, I can beat this tumour.
I keep thinking like this so that I don't feel like a prisoner in my own body. Otherwise, it would be very easy to sit at home and give up.
All the training I've done my whole life wasn't to win an Olympic medal. It was actually to stay alive.
I was paralysed from the neck down, I couldn't really use my arms and I had to completely learn how to walk again. I've had to find the drive to rebuild myself, through extensive physio and exercises like boxing, cycling, weights, strength training and the rowing machine. I've had push myself back into one of the hardest sports in the world to get back to top fitness. It takes a lot of emotional and mental strength.
The hardest part - and the hardest thing I've ever done in my life - was getting to the starting line again. It was even harder than racing. I remember telling myself: "You know, the next 1,000 metres is going to hurt. But nothing can come close to the pain when you're told you might die."
To cross that line at the London 2012 Olympics, I remember taking that last stroke and collapsing back in the boat and thinking, "Thank god that's over." And we won gold.
Rowing saved my life and gave me my dream, winning a gold medal in London. But my journey in rowing hasn't been about leaving without a medal - it's been about leaving alive.
We're so hard on ourselves as human beings and I know I'm very hard on myself. I think sometimes we should all pat ourselves on the back and say, "Hey, you're doing well."
I try to engage in every day. I want to look in the mirror every morning and say, "Hey, if this was the last day I was alive, what would I do with this last day?" so I try to do things that enrich me and really fulfill me. Ultimately, that's sport and movement and being around good people.
According to performance psychologist Tom Bates, Smith's drive, resilience and determination to succeed after this potentially major career setback are all part of the positive reframing that people can do if they suffer an injury that takes them out of their sport or favourite exercise.
"There's a lot of common challenges that people experience once they have an injury," says Bates. "The first one is doubt and uncertainty. It's a difficult time. Your confidence can drop. There are unpredictable elements to the recovery process. This all threatens a person's livelihood."
"If it's who they are, if they're connected to a team, there's a social element as well: feeling like I don't receive that energy and inspiration that I once did socially and emotionally. Perhaps that leads to some denial or a refusal to accept the situation as it is. A physical injury doesn't have to mean a mental, emotional or lifestyle injury, but people will sometimes focus on the negative perceived effect on their lives and the thinking that if I'm injured, I won't be able to do this or that."
Bates also encourages people who are feeling down about an injury to become aware of the false and negative beliefs, the ones keeping you locked into a negative spiral.
"The way we think defines the way we feel. The thoughts that we have either help us and empower us or they don't. The first step is to become aware of the thoughts that don't serve you and replace them. Don't pay any attention to the disempowering limitations, they can destroy. Belief is the enemy of doubt, replace those beliefs of disempowerment with confidence and just do something," Bates advises.
"One small step every day can improve other areas of your life (social, nutritional, etc.). Channel your energy into something constructive. Take control of what you can do in your life and don't let what you can't do get in the way of what you can," he advises.
Smith continues to train, pushing and testing the limits of his fitness even further, and has added another impressive feather to his cap: joining British Cycling's Paralympic Academy programme, which he's been involved with since 2014.
I continue to train, pushing and testing the limits of my fitness: in 2014, I joined British Cycling's Paralympic Academy programme.
All the training I've done my whole life wasn't to win an Olympic medal.
It was actually to stay alive.