Of the lessons I ignored
If someone confides in you something secret don't use it against them or throw it in their face when you become angry, they will lose respect for you and if someone does that to you remember that they're only human just like you and so you should forgive them as this will endear them even more to you.
We learn from our mistakes more than we learn in advance of them.
So be patient with one another.
Besides, you will need the generous arm of forgiveness too for the wrongs you are yet to do.