Now, who do we learn good things from? Well, the answer is obvious - Good people!
Not just from good people, you can also learn to do good things from Bad people.
See, if you're working, and if you had the opportunity to work with more than one Boss/Manager, you would have realized that some times you get a difficult boss, or may be sometimes your usual Good Boss, turns into a bad one.
So what do learn from them? Lets just say, you need to learn from them WHAT NOT TO DO when you become the boss!
Still confused? Let me try again. See, lets say you don't like a hypocrite boss. For example, the boss always comes late but tells you to be punctual. Or may be he violates ethical principles, but gives you lectures on moral values, then what do you learn?
You learn to not behave the same way with your Juniors! See, the point is, if you don't like something in him (and it includes what your colleagues may not like about your Boss) you should understand that people will not like it, when you repeat the same.
I have often seen many people (may be even I do it and may not yet know it) do the same things they hated about their boss. They might be unaware of the fact that they treat their juniors the same way, which they hated when their boss treated them.
So lets just remember what we did not like as Juniors, so that when we are the boss, our Juniors need not complain the same things about us, as we did about our previous bosses.