But here is the list I've ended up with: 20 stuff ups by 20. Try them at home at your peril.
1. Panicking because I have no idea what I'm doing: The moment I realised you never "feel" like an adult was almost comical, after spending years waiting for it. No one feels in control, and if they do, it's a temporary illusion.
2. Not taking opportunities: It's incredible how much it can play on your mind for years to come. I certainly regret things I didn't do but should have more than the things I shouldn't have done, but did.
3. Being too critical of myself: There is rarely a need for it, and it's pretty uncommon anything positive comes from it. I'd never verbally slap a mate around. I need to treat myself the same.
4. Being too critical of others: Everyone is just trying to get by in life. I've had enough moments now where something going on in my life has caused me to not conduct myself perfectly, that I've learnt to write off others' behaviour as the same thing. Everyone is fighting a battle you know nothing of. Show compassion.
5. Worrying about what other people thought of me: The ability to relinquish your fears of how people see you, while still being determined to be the best person you can be, is incredibly freeing. Learn to laugh at yourself.
6. Not treating my body well enough: Before my cancer, I lived like a normal teenage guy.
It's not a bad thing, and I'm not saying you shouldn't for a period of time. Enjoy it, but know when to draw a line.
7. Not opening up to people or talking about my emotions: Mental health is something I'm passionate about, and something I'll talk about a lot more in time.
I know now the value of asking for help when you need it, and how tough this can be.
8. Not listening to advice: Surrounding yourself with good advice makes you infinitely more powerful.
9. Not dedicating enough time to those who are important to me: It's almost a cliche. But particularly over the past few years, I've learnt the importance of being close to those who mean something to you.
10. Discounting the value of friendship: I spent many of my teenage years being solitary, not feeling the need for the camaraderie that school and team sports offered. I've since found human connection to be so much of what makes me happy.
11. Being afraid of the future: Yes, bad things will happen to you - adversity is inevitable. But good things will happen too, and good things can come from the bad ones if you so choose. As a kid I worried my knees were going to bend backwards. That was a colossal waste of my time. So is worrying about death.
12. Being afraid of things that won't matter to you in the future: Sweating the small stuff. I would've spent far fewer nights laying awake looking at the ceiling over trigonometry if I had known this.
13. Wanting to be like other people: It's great to have idols and role models. It's not great to be envious. I should have been more okay with being me even when I felt uncomfortably different, because being okay with being different is easier than wishing you weren't like you are.
14. Not apologising earlier: There's very little wrong that can come from saying sorry.
15. Conversely, not standing up for myself: Being okay with taking s*** just because it doesn't bother you is not a valid excuse.
16. Letting my pride win: If I were listing specific mistakes, there would be far more than 20.
17. Not laughing enough: Laughter can get you through just about anything. It pulls people closer and makes life easier.
18. Thinking possessions equate to happiness: Lifelong happiness doesn't arrive in a package with the things you covet. Appreciating what you have will make you happy.
19. Thinking I could get away with lying: I was shocked to learn recently I hadn't fooled my parents into believing that it wasn't a 7-year-old me that trimmed chunks out of the cat's fur. Deception is the quickest way to lose people's trust and your self-respect.
20. Ironically, dwelling on mistakes of the past: Wishing I said or done things differently. Mulling things over and over achieves nothing. Fix what you can; make peace with what you can't; learn from it; don't repeat it; walk forward.
I found it cathartic to write this list. Compassionately examining your mistakes and weaknesses can help you accept them and see them for what they are - lessons. Value your lessons. Use them to forge a future direction that puts past experiences to use. Or keep making the same mistakes. It's up to you.