My brain can be very stubborn, negative and self defeating. What are ways I can try to change this?

An example is that right now I am pursuing becoming a teacher and I think there are many good reasons it will be good work for me: I enjoy the subject I wish to teach (math), I am pretty good at it, I enjoy watching others learn and grow and can be patient with the process, I've thought a lot about what made learning unenjoyable for me and seek to improve those things, I believe I can make a positive difference in people's lives, etc.
However, for some reason my brain filters out all those positive things about the job in assessing how it defines me: There's doubt in how much respect I will receive, it's difficult to measure the impact I might really have, how valuable can I as a (public school) teacher really be if there is a limit on how I earn compared to other professions, how many people would really look up to me if all they knew was that I was a math teacher.
Now I want to make it clear that it's not that I believe teachers don't have an impact or that they are less valuable because they earn less. I also don't believe how much a person earns defines their value and don't care about earning that much money (I am rather frugal and don't really have many things I want to buy). I fully realize that comments regarding the aforementioned topics are generally subjective opinions and anybody can have a different take on them. It's more the fact that I cannot seem to place that much value into my own opinion and be truly comfortable with it. This seems to be a common problem for me. It is common to hear that I could maybe try to place less weight on other people's opinions. However if I knew how to do that, this wouldn't be a problem! I also don't necessarily believe there are much better choices for me than the ones I choose, but I can't seem to feel any of the positivity that may come from my good reasons or at least embrace my decision without a reluctant acceptance.
Another way to describe it would other people seem to be able to control the volume of their feelings regarding the negative sides of choices they make. I feel like my negative feelings are on high and I don't really know how to turn it down. I've tried meditation and have seen a therapist before. Those have sometimes helped, but for the most part the bigger picture hasn't changed.


Source.