The very best sportsmen 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.
Having started off with Steve Backley, we now move on to squash legend Peter Nicol.
We also want to know the single most important thing you've learned from sport - follow the link to the 606 page to contribute.
ALWAYS APPRECIATE WHAT YOU'RE DOING
I always wanted to win everything, and if I lost, I found it very hard to be happy - I'd want to go back and work out how I could be better, how to beat that person.
It took me a while to learn that you have to enjoy the process, appreciate the playing, the training, the winning and the losing.
I remember losing in the final of the 1997 British Open to Jansher Khan, in two hours, seven minutes. I was exhausted, there were loads of decisions by the referee which I thought were wrong, and Jansher was getting in the way, blocking me and causing all sorts of problems.
But within a minute of coming off court, I was okay. I'd done the best I could, I'd given everything I had, and I was content.
When I was younger, if I lost, that was bad. But it's not - it's part of the process. Appreciate the journey, win or lose.
LOOK AFTER YOURSELF PROPERLY
Do what's right for you at the time - don't just stick to the strict guidelines.
Won World Open 1999
Won British Open 1998 and 2002
Commonwealth gold medallist 1998 and 2006
Won three consecutive Tournament of Champions titles
World No.1 for 60 months, including 24 months in a row
About four years ago I was going through a tough time, because I was changing from being purely a squash player into trying to have a life too. I was trying to find out who I was.
I went to a tournament in New York, and I wanted to play squash, but the most important thing was that I wanted to have some fun.
I was out till 5am every morning, just enjoying myself. I'd get up at 2pm, have a light hit, rehydrate, have a decent amount to eat and go back to bed.
I'd wake up at 6pm, put my squash kit on and go out and play. I'd finish my match and go straight out.
That was the only tournament when I won winning every match 3-0.
Now you couldn't keep doing that. But I was so happy and relaxed that I was able to go out and enjoy myself and play freely.
Five matches in a row, all without dropping a set - it was the best tournament I ever played.
ALWAYS LOOK YOUR OPPONENT IN THE EYES
You don't have to do this in an aggressive or confrontational way - just have a look in there to see what's going on.
In the 1996 World Open in Pakistan, Ahmed Barada was beating me badly. I remember thinking, I've got to do something to change this.
One thing I did know was that, because of the way he played, he annoyed people, and the other players didn't like him. He was quite a lonely character.
So after each point, I'd just stop and look at him. I'd just stare at him for a bit and see what was going on with him.
After the fifth or sixth time I did it, he stopped and said, "What? What? What are you looking at?"
And I knew at that point that I had him. It sounds cruel now, but that's sport - it's a battle.
He did many things that weren't so nice to win matches. One time, playing in Cairo, he scissor-kicked me across the back of the legs and got away with it.
It was by looking at him, by showing myself and also seeing what he had to offer, that I beat him. He retired soon after that.
LISTEN TO EVERYONE
I would even listen to club players. Because they could only see things at a simple, basic level, they were sometimes capable of spotting things that coaches couldn't.
A couple of times club players have come up to me and said things like, 'Why do you do that thing with your back foot when you go to the front left corner?' and I'd say, 'I do what?'
I'd look at video footage and realise 'ah, that means I'm not moving so well out of there'.
A simple conversation with a club player would allow me to identify something I'd been doing all my career, adapt it and improve as a result.
You don't have to take on everything that's said, but understand yourself enough to filter it through and do what's best for you.
KNOW HOW AND WHY TO PREPARE
If all your preparation has gone absolutely perfectly, then great. But most of the time, it won't have done.
You need to prepare properly for the state of mind you're in.
When I played the Super Series, I was playing poorly, was extremely tired and had lost in the first round of the last two tournaments.
So what did I do - go out and practise, stretch, or conversely just relax, sleep, and turn up five minutes before my game, pick my racquet up and walk onto court?
I chose to do the latter, because physically, emotionally and mentally I couldn't have done the former properly.
I understood where I was coming from, what I was capable of and what I needed to do for myself. And it worked - I won the tournament.
EXCEL THROUGH ADVERSITY
You're always going to be faced with problems. I think I played a handful of matches in my life when I was completely ready and prepared to perform at my best.
You have to understand that adversity to then excel. In Cairo for the World Open final, there were 5,000 Egyptians supporting Ahmed Barada and five people supporting me.
What should I do - try to block them out? That wouldn't have worked, because eventually they would have got through to me.
So what I did was accept that fact that they would be supporting him, and use that to my benefit.
Any doctor or physio or expert in sport science will shout at you never to do this - but to me it's hugely important.
If you don't do it, you'll never know your limits.
In 1995, before the World Open in Barcelona, I didn't eat for five days because I had food poisoning. All I could manage was sugared water.
People would say, well you shouldn't have played. But I got all the way through to the semi-final, and was 1-1 with Peter Marshall. I lasted an hour, and then collapsed.
I was then ill for the next six months. Now that's not good, but it is an example of how you can keep pushing yourself.
Get past the limits that you're aware of. And then push again.
BE COMPLETELY HONEST
It's the most important thing as an athlete. If you're not honest, everything else falls apart - training, matches and preparation.
In training it's about knowing exactly what is going on at all times, and being your own harshest critic whether things are going well or not.
If you don't do that, it's going to come back to haunt you, whether it's one point in a thousand - that could be in the World Open final on match point.
But it will come back.
If you can be yourself, you can achieve whatever you want to achieve. But if you're not, and you're a liar, you make it very hard for yourself.
Nicol was world no.1 for 60 consecutive weeks
I found that if I tried to be someone else - for example, be really aggressive, or be flamboyant - it didn't work.
I remember playing Rodney Eyles, an Australian who was a real fighter.
He wanted to be confrontational - he'd come up to me and say things. In return, I would just look at him.
We had three matches in a row. He won the first one, but only because he took a rest in the fifth set when he wasn't allowed to.
I was upset with that because I felt he'd cheated me out of it. The second one I won 3-2, although it was a really tough one again.
If he won the last one, he would go to number one in the world. He was well up in the match when he cramped, and he actually couldn't take his hand off the racquet.
He was himself and I was myself, and we both respected each other, so when he looked up at me with cramp and asked me to get his hand off his racquet, rather than going to hide in the corner, I did it.
In training, if you're meant to be doing 10 sets of something, do 10. Or 11. Or 12. But never do nine.
If you do less, that's the start of a sharp decline. If you don't finish a session, you might as well retire then and there, because you're done.
There will always be excuses - whether you're injured, tired, have done something tough the day before - whatever. It's all irrelevant.
I never gave any excuses, and I wouldn't expect to hear any from anyone I work with.
You should also always finish your match or competition, especially if you're injured or ill or losing badly.
I've seen so many players against me just give up. They knew they weren't going to win, so they created an illness or injury.
But out of respect for yourself as much as anything, you should go through that process, to stand there at the end having been thumped.
Shake your opponent's hand while looking into their eyes. Finish the match, whatever the circumstances.