What Sithy thing did we learn?

[Fifthrate]

I learned it's easy to choke the woman you love when you turn to the dark side to keep her alive.

[arutha1000]

I learned that if you lose once (Yoda vs Palpatine), then you should just give up. Ignore the fact that you could save the galaxy. Who cares that Obi-Wan and Yoda could team up and take him out, especially with Vader out of commision. If you fail once, just go into exile and give up.

[Plastic Self-Cleaning Duck]

Something I learned but forgot to mention....

It's alright that Obi-Wan can't kill Anakin/Vader because "he's like a brother."  But there's something wrong with Luke if he doesn't want to kill Vader after he knows that he's his father.