It helps to discuss problems with someone, even if they aren't an adult. It helps with getting different perspectives, because we all have blind spots.

If you're determined to go it alone, I at least recommend Rubber Duck Debugging.

I couldn't tell you how many times this technique has helped me work out what was wrong my code / problem. The majority of the time it's something simple.

Well, as an adult, you probably don't want to hear from me, but a healthy amount of self reflection will go a long way. When you make a mistake, think about it. What happened? What went wrong? How can I avoid this in the future? As long as you can look critically at your actions, you can learn a lot about the situation and how you reacted to it.

If the reason you don't want to speak to an adult for guidance is because there aren't any you find trustworthy or who know how to communicate effectively with you, I think the best way to learn from your mistakes is to look for the patterns around them. Then, shift your perspective from being the person who made the mistake to being someone on the receiving end of it--walk a mile in someone else's shoes to understand them better and all that. For me, I found getting to know myself a really important part of this: I had to know what I was like when I felt my best and worst to recognize the things that went wrong before I made a mistake. It took me until adulthood just to recognize that I have a slow-to-warm personality and tend to be inflexible, which means that any unexpected changes really fuck my shit up and can lead to me making mistakes because I feel like I'm scrambling to adapt. Give me an extra minute or three to live with it and I'm fine; don't give me the extra time, and I'll probably be nasty towards you even if you don't deserve it. Recognizing those patterns in my own behavior lets me say, "Hold on, I need a few before I can do what you want" instead of, "Are you fucking kidding me? You're doing this again?" (which, it turns out, upsets the people who are so ready to demand I do something flawlessly and on their schedule instead of mine, lol).

Looking for the underlying causes of mistakes is like tracking down clues to solve a mystery. Maybe you missed a throw because your hands were sweaty and the ball was slippery, or maybe you miss a throw because your mind was busy trying to work on a different problem while you were throwing a ball. Maybe an unexpected gust of wind blew the ball in a different direction than you were expecting it to go; mistakes aren't always because of things that we can control, so it's important to be fair and kind to yourself when you're looking for these patterns behind them and recognizing when something isn't your mistake.

It's way too easy to get wrapped up in the idea that making mistakes makes you a failure or a bad person. Nah, they just mean that you're doing something you're not used to doing perfectly. Nobody just hops on a bicycle and rides off into the sunset on their first try. It's a skill that takes practice. There are tons of skills like that that most people don't think of as needing practice before you get good at them: making friends, being a good friend, creating emotional boundaries, saying no, saying yes, asking for help, washing dishes, fixing a leaky pipe, emotional regulation, apologizing, forgiving, driving... it's a long list, but you get the idea. Being bad at a skill is a temporary thing, and making mistakes is how you figure out how to improve.

Look at the mistake. Ask yourself why you made the decisions that led to the mistake. Ask yourself what should you have done to avoid making that mistake. Remember this and don't make the same mistake again.

It's difficult to learn from a mistake without an external reference point. To learn from a mistake, you first have to recognize that you have made a mistake. How will you do this on your own? Presumably if you could recognize the mistake, you would have avoided it in the first place.

Second, even if you know that you made a mistake, it's hard to know for sure what the mistake was. Say for instance that you did some step in a task badly, and you can see that the results were poor, so you tell yourself "I'll do this better next time". But maybe the issue wasn't in your performance, but that you were rushing - you didn't give yourself enough time to prepare and then you didn't take enough time to do the work properly. So, the problem isn't in your execution of the task but in your planning for the task.

It's very difficult to recognize this sort of thing in your own work without some outside perspective (what does good planning look like in this context? how would you know without someone else's guidance?), and you have to be very self-aware and also collect data on your own work so that you can review and analyze it later (which is time-consuming, and you might be re-inventing the wheel, when you could've just asked for guidance from someone with experience).

Frankly, this is why writers benefit from editors. You can't effectively edit your own writing - you'll either be too critical and never actually publish anything, or not critical enough and publish garbage, or both. In any case the problem is that you're too attached, too close to your own work to judge it fairly - you can't see the forest for the trees. You need the perspective of someone outside.

Rather than trying to exist without guidance, you should learn to recognize sources of good guidance and pay attention to them, and keep them in your life when you find them.

In order to know that something is wrong, you have to know what it's like when it's right. In order to know how not to do it wrong, you need to know how to do it right. If you haven't experienced the process of doing it right, then you need guidance.

Also, also, very important, always remember: It's possible to do everything right and still fail.

Flow chart it. And write it down. Don't just do it in your head the first few times.

I did this -> this happened. If I'd done that -> this would have happened. Conclusion: I should do that in such situations.

Even if you're not accurate in the beginning, this is what will get you into the mental model of analyzing your mistakes and assessing different paths. Once you get the hang of it on paper, do it in your mind.