A cool tip I've picked up on is to have a label in your inbox called "feel good" (or whatever). Then tag the emails that make you feel good, whatever they are. For example, in mine I have an email of my former academic advisor congratulating me on my MSc defense, the first email sent to me by one of my mentors which led me to move to CA, etc.
Ideally those emails will span a period of years, if not decades- it brings a nice perspective on life during stressful times.
I believe the point of the black box is to not be dependent on others for your happiness. Needing external validation to feel good about yourself is a serious mental issue. But, to you, it shouldn't really matter what I think ;)
Needing external validation to feel good about yourself is a fundamental characteristic of human psychology. The black box thing is about picking and choosing whose validation you care about and whose you don't. That's healthy. Genuinely not caring what anybody else thinks sounds more like sociopathy.
Ideally those emails will span a period of years, if not decades- it brings a nice perspective on life during stressful times.
That can be your little "black box" :)