A bad manager teacher you how to be a good one.
A bad relationship teaches you how to love.
I get what you're trying to say but I don't agree. A bad experience cannot teach you how to make it better for someone else, only good experience can do that.
A bad expereince can teach you how to not do things, and that is equally important. But it also leaves vaccum for what could have been a learning experience. If you're smart you'll find out better ways to do it, either on your own or through other people, but simply knowing what not to do is not enough.
Why? Because unless you expose yourself to the possibility of just how it can be, you'll improve upon your bad experience by say 5% or 10% and think you are doing it right. Of course there's no binary right or wrong but you'll see any imporvement as positive and potentially continue to be a bad experience for someone else.
When I resigned my first job, my then manager and now a great colleague showed me so much kindness and empathy, it made me cry. I called up my friend unable to speak, saying things like I am such a bad person, such a bad manager because this kind of kindness has occured to me. I have never been rude to my juniors but I have also never been so empathetic, because I had never expereienced that kind of kindness myself. I didn't know something like that was possible or even how impactful it was. My friend calmed me down and said, "you're not a bad person." Ofcourse she'll say that. "Now that you have expereinced this, you can learn from it. It's good that you had this experience. You can replicate it the next time while talking to a junior. And you'll probably not get it right the first time, but you can now improve everytime since you have a benchmark.
That's just one experience. I can give a hundred examples like this. I am not throwing around a random figure, I really can. We need benchmarks of positive and good things just to know how much potential there is still. That is not to discredit whatever 5%- 10% improvement you are at crurrently, but simply to give you a realistic idea of where things are.
Contrastingly, everytime I've had a bad experience and I have been in a similar situation? I have behaved in a somewhat similar manner and just removed the obvious red flags from my behaviour. I have heard myself and plenty of other people say, "We had it worse, why are they crying." Because they fucking expect better. And they are right to expect better. It is not their fault you had a bad experience. And theys hould not be subjected to a similar experience just because you had to go through it or deprived of something that you could not have for whatever reason.
As a society, we work so hard to make things better. To improve the standard of living. Its a good thing that people younger and junior to you have it easy. Do you not wish you had that too? Stop depriving others of a good experience just because you couldn't have it. It's difficult, I know. There's this unexplainable jealousy and anger "Why should they get it when I didn't?", but once you get past it, you'll see why.
A bad manager does not teach you how to be a good one.
But a good manager sets a standard so high, nobody will dare fuck around with you in the seniority and more importantly, you wont fuck around with your juniors.
(My unnecessary urge to end this with 'Amen.')