The very best sports stars are forced through physical and mental tests that would give us mere mortals nightmares.
But the consequence of those experiences can be a unique insight into sport and life in general.
In a new series, we're talking to British sportsmen and women notorious for taking their sport, preparation and strategy to incredible levels.
Each of them has looked back on their career and identified the 10 key lessons their life in sport has taught them.
Javelin star Steve Backley and squash supremo Peter Nicol have already taken part. Now it's the turn of around-the-world sailing legend Ellen MacArthur.
We also want to know the single most important thing you've learned from sport - follow the link to the 606 page to contribute.
NEVER GIVE UP
Never give up is one of my lessons because of an experience in a race I did in 2001.
We were sailing from France down to the Mediterranean - we were not doing brilliantly but we were in the leading pack.
MacArthur sprang to prominence in the 2001 Vendee Globe race
We found ourselves second for the last few days and literally, in the last 10 minutes of the race we overtook the lead boat when no-one thought we would and slipped across the finish line first.
It just goes to show it really isn't over until it's over and you should really never ever give up.
BE AS FULLY PREPARED AS POSSIBLE
For me, being fully prepared is the mental state in which you start a race or a record attempt.
It's knowing you could not have done more to be ready, and that's having every little spare part on the boat, being physically fit, having sailed thousands of miles on the boat in training.
It's the feeling that you are ready, it's time to go and it's time to get on with it.
TAKE STRENGTH FROM THE TEAM AROUND YOU
The best feeling I had in the whole around-the-world record was the feeling of team work.
And that's bizarre to think that you've raced around the world to break a record on your own but actually the biggest thing was the team.
2005: Smashes Francis Joyon's solo round-the-world record by 33 hours. Sets new mark of 71 days 14 hours
2004: Misses out on west-east transatlantic record in new trimaran B&Q by 75 minutes
2003: Fails in Jules Verne round-the-world record bid when mast breaks
2002: Awarded MBE; Wins Route du Rhum in record time
2001: 2nd Vendee Globe solo around-the-world race
2000: 1st Europe1 New Man STAR transatlantic race
1999: BT/JYA Yachtsman of the Year
1997: 17th in Mini Transat solo transatlantic race
1995: Sails around Britain alone on 21ft yacht.
Born: 8 July, 1976 in Derbyshire, England
The amount of hours and passion that those guys and girls put in before the start was extraordinary and they made the project.
Although the images you see are just one person finishing an around-the-world record or race, the reality is completely the opposite. It's about the team effort. It's about the team that designed the boat, built the boat, prepared the boat and you trained with on the boat.
Those people are as much a part of the team as you are. It just happens that you are the person that has to go in front of the camera.
IT'S GOOD TO BE FRIGHTENED, IT KEEPS YOU ON YOUR TOES
I always think it's good to feel afraid on a boat and if you don't feel afraid, something is wrong.
In certain situations it is human nature to feel afraid and you need to be worried so you don't make mistakes.
If you need to stay awake sometimes, that fright really helps you do that in a storm or in a difficult situation or a time when you have to fix something.
When you leave the deck, when you have to go up the mast, it's a bit like going on a mission and that mission in the round-the-world record took two hours, in the Vendee Globe it took three-and-a-half hours and it's a pretty stressful mission.
DON'T LOSE SIGHT OF YOUR ULTIMATE GOAL, STAY FOCUSED
It's easy when you are out there to get frustrated with a small problem.
But, ultimately, the best way to get through that small problem is to look to the future and the finish line and to think, 'whatever I'm going through now, tomorrow is another day, and we're heading to that finish line'.
That helps me hugely to stay motivated - looking forward and thinking through our problems.
MacArthur broke the solo round-the-world record on B&Q
When I was heading down the Atlantic on the round-the-world record I had a problem with the generator. I had one main generator to power electrics and a back-up. The main one was faulty and using too much oil to make it around the world.
But I had to see through to the other side, I had to see through the bad weather and the storms and try to work out how to get through the Southern Ocean using that engine, rather than worry that it wasn't working and bailing out.
NEVER UNDERESTIMATE THE POWER OF THE SEA
The power of the sea can be just extraordinary and you should never underestimate how bad it can get.
Sometimes you can be in a really bad situation but you always have to look that next step ahead; is it going to get worse? Can it get worse? How will it be when it gets worse and how will we cope with it? You always have to be ready for that and it can be really, really evil.
One example of a really bad time in the Southern Ocean was on Christmas Day when I was doing the record attempt.
The weather was pretty bad. I was in front of a big storm and I had to maintain 20 knots to stay safe because behind that storm were 80-knot winds in another direction.
If I had broken something then, three hours later I would have probably broken up the boat. It couldn't have survived those conditions and you're living with that all the time. You're definitely not underestimating the sea in those circumstances.
STAY TRUE TO YOURSELF AND NEVER LOSE SIGHT OF YOUR VALUES
When I finished the Vendee Globe in 2001 I was 24 years old and suddenly went from being nobody to being somebody who people knew. That's quite a big change for you, personally.
Obviously sailing is your passion, you're focused on that and that's what drives your life but you also have a life on land. You have a family and you have friends around you.
That's really important to me because I don't want to change as a person.
I don't want to change as a consequence of the things that are changing around me. It's really important to stay who I am and keep my feet really firmly on the ground.
NEVER FORGET THOSE WHO HELPED YOU ALONG THE WAY
The journey to get to where you are is really important and although now I've had the chance to break the solo non-stop round-the-world record in an amazing 75ft trimaran, it wasn't always like that.
I came from a school in the middle of nowhere in the countryside and had to find those first sponsors, and those first people who just helped in anyway they could.
I never want to forget those people. It's really important for me to stay in touch and keep contact because it is a journey and you couldn't be here without the past.
There's a guy called Jim Hyland who helped me at the weekends. He worked at the marina where I used to live in my tiny boat. He helped me when I had no friends, he helped me put up my mast and get my boat in the water.
Another friend called John the Bowman used to bring me tea cakes and fresh milk when I was living in my hut.
I had no money, I was really struggling and trying to find a sponsor and that was my focus. It's people who just think about how you are doing and how things are going.
ALWAYS TRY TO HAVE FUN
When you're on a boat in a really difficult situation with a team of people and it's really, really hard, if you can get a little giggle from someone in that situation you'll have so much more chance of getting through it.
Fun is really important, both at sea and on land. When we were preparing the trimaran for the round-the-world record, we were down there in the boat at 4am before setting off from New Zealand.
MacArthur sliced 33 hours off the solo round-the-world record
There was still a giggle going on, people were still enjoying what they were doing and when you're under pressure it's a fantastic release.
I was racing across the Atlantic a couple of years ago with a Frenchman and we were in a 40-knot storm - it was pretty horrible, with big waves, just really hairy.
We were right down in the front of the boat trying to get the storm jib, which is the sail you put up when there's lots and lots of wind.
And literally, we were bouncing off the bottom of the boat and then hitting the roof. It was just like a bouncy castle. But we both ended up in fits of hysterics because although it was really serious, there was a funny side to it.
ALWAYS DO YOUR BEST
At the start of races I've often been asked if I'm there to win.
I can never say I'm there just to win the race, I'm there to do my best and enjoy what I do.
But if you finish a race or a record and you've given everything you can and you've done your best, what more can you ask for?
If you've won, that's fantastic. My objective is to give everything when I've crossed the finish line.
When I did the Vendee Globe in 2000 it was my first non-stop round-the-world race and I really did give it my all.
I didn't win, I overtook the leader at the equator on the way back up the Atlantic.
Then I hit a submerged container in the water and ended up breaking the daggerboard and I finished 24 hours after him.
But I never gave up and I did my best and at least when I finished, I knew I couldn't have done more.