I was taught (when teaching for the military, actually) that leadership/teaching/etc. often talk about toolboxes but neglect a VERY important one.

You shouldn't just have a toolbox of things you've picked up from your best examples, that you've been taught, etc. It's possibly more important to have another toolbox of broken tools from all the terrible bosses, reactions to situations you've witnessed, etc.

This way when you go to do something and it's not in your toolbox, you can pull out that box of broken/bad tools and see if it's there. Otherwise we perpetuate bad leadership (and teaching IS leadership) through intentional ignorance (forgetting the lessons those bad situations gave us).