After 9 years in software, I switched to still being in software but for a noble purpose (mobile money in Africa), and then to nebulous indirectly-x-risk-related research work. My guess is my experience will not say much about yours. 

When I made the change, I didn't particularly feel like I was trusting myself more. My first reason is "the research on M-PESA in Kenya is too strong to argue with", although the part where I'd read that research for ~fun and trusted my interpretation maybe counts as trust in myself. But also: I wasn't happy at my old job and would have been leaving anyway, my new job had a much better set up for me even before mission considerations, everyone I knew supported the change (and my later move to independent work). 

The move did improve my sense of how valuable I was and how much I was allowed to invest in myself. I think it's good that that happened but it would have been better if I hadn't needed a mission to justify it.

You've talked about "becoming an adult" and "trusting yourself (to make world-improving plans)" as almost synonyms, and I think that's a mistake. If I was going to make a road map to impactful and responsible adulthood it would be as follows (hastily written, undoubtably missing stuff, etc):

1. be stable and functional: take care of your health, your finances, and your housing. Be capable of showing up on time and keeping comittments. Have enough savings [EA · GW] to weather emergencies and transitions without worry. 
2. Be able to be a decent friend, family member, and possibly neighbor (which includes creating enough slack in your life you have capacity to help people). Don't be a parasite on any system. 
3. Work on other people's projects
   1. Develop valuable skills, if you haven't done that for #1 
   2. Develop the skill of being useful to a boss, who may make decisions you disagree with and won't justify them to you. 
      1. This includes knowing when and how to ask questions, push back on bad ideas, shut up and do work you disagree with, and refuse when necessary.
   3.  Develop your sense of taste so you can figure out who is worth deferring to and who isn't
   4. Develop your ability to coordinate with peers, without the boss/teacher managing the process.
   5. Develop your ability to work with people even when they are very annoying. 
      1. Twice in short succession I had a big dispute with someone w/i X-risk community, and we went away thinking very poorly of each other. Not a big deal, there was no reason to think we'd ever have to work together. @Raemon [LW · GW] (also the author of Earn-To-Save) told me that my complaints were legitimate but both people had valuable skills, and saving the world necessarily involved dealing with people at least that annoying. 
         
         So I did mediation with both. One went great, we are now friendly and have a lot of respect for each other. The other was a less smashing success but was good enough that when it looked like our projects would intersect I felt annoyed but not doomed.
4. Gradually expand your sense of taste and ability to work autonomously. Any good boss wants to give you work off their plate, they will be delighted if you gradually work your way up to being an independent agent they can give vague instructions to do 
5. Eventually you have the choice to your found your own thing (with or without co-founders) or work for someone, and the wisdom to know which will best accomplish your goals. 

Over the last two years, I discovered LessWrong, learned about x-risks, joined the rationalist community, joined EA, started a rationalist/EA group house, and finally left my comfy high earning crypto job last September, to start working on AI safety. During this time, I definitely felt multiple switch of taking on different kinds of responsibilities. 

The first responsibility I learned, by reading HPMOR and The Sequences, was the sense that more was possible [LW · GW], that I could achieve greatness, become as cool as I ever wanted, but that it needed actual work, that I was not on the right path to achieve it, that I would need to take risks and that I could not count on any of my then friends to help me with it. It was at this time that I took responsibility over what my life would be like.

I joined the rationalist community somewhat quickly, and after a few months ended up creating a rationalist group house. There, I spent lots of time with people very different from those I spent time with, in no small part because they questioned my beliefs. I realized lots of the factual knowledge I got from the Internet or from school was incomplete or flat out wrong, that the procedural knowledge I got from my parents and common culture was deeply suboptimal, that strong and counterproductive emotional patterns were driving me a large chunk of the time, and that generally my epistemics were broken, which prevented solving the other problems. I realized I could not trust anyone to give me correct knowledge, to show me the right way, even on the most basic stuff. It was at this time I took responsibility over my cognitive processes and beliefs, because blind faith was not a reliable way to navigate the world.

Leaving my job for AI Safety definitely felt like jumping into the unknown. For the first time in my life, I cared about achieving a goal that was wildly above my level. I finally had something to protect [? · GW], and was taking active steps each day towards getting better. It felt like taking the responsibility of shaping the future like I wanted. I realized nobody else would do it for me.

Working on AI safety full-time also led to a large increase in the amount of stress I experienced, as working harder and caring more than I ever did exposed lots of flaws that were never a problem when I was just going with the flow. I can give more details on the issues I experienced, but basically I was terrible at noticing issues and kept ignoring my emotions [LW · GW], nearly leading to burnout twice. I realized nobody could manage my internal states except me. It felt like taking responsibility over my motivation, my happiness, my reactions to any event. This is still a work in progress, though.

When I first read HPMOR, I expected that taking responsibility was just a single jump you had to take once. Now, it seems to be a succession of realization, where the tools I had been given proved to be insufficient, and I had to take upon myself to reforge better tools. I'm actually looking forward to the next realization now. I hope you and I have the courage to continue down this road.

This isn't quite what you asked for, but I did feel a related switch.

When I was a kid, I thought that probably people in positions of power were smart people working towards smart goals under difficult constraints that made their actions sometimes look foolish to me, who knew little. Then there was a specific moment in my early 20s, when the political topic of the day was the design of Obamacare, and so if you followed the news, you would see all the day-to-day arguments between legislators and policy analysts about what would go in the legislation and why. And the things they said about it were so transparently stupid and so irredeemably ridiculous, that it completely cured me of the idea that they were the thing I said up above. It was clear to me that it was just a bunch of people who weren't really experts on the economics of healthcare or anything, and they weren't even aspiring to be experts. They were just doing and saying whatever sort of superficially seemed like it would further their career.

So now I definitely have no internal dissonance about trusting myself to make decisions about what work to do, because I don't take seriously the idea that someone else would be making any better decision, unless it's some specific person that I have specific evidence about.