1. Pride goeth before a fall.
This is shown in many characters. Clearest of all is, of course, Anakin/Darth Vader. His pride in his Force-strength leads him to defy his superiors consistently, leading to his eventual downfall and the very thing he sought to avoid - the death of Padmé.

Second is Obi-Wan. He insists, against the direct order of the Jedi Council, on training Anakin. And (in Paul Harvey tone) you know the rest of the story. This could also be taken under the second heading:

2. "Bad decisions suck - for a very long time."

(The brilliant quote is courtesy of a dear friend.) It is exemplified, (or can we say defined?) again quite obviously, by the beautiful but unfortunate Padmé Amidala, whose life seems to be a series of bad decisions. (Perhaps this is why fourteen-year-olds shouldn't be Queens, although this one's bad decisions are mainly a result of her naiveté, which is proven by her listening to very bad advisors, a.k.a. Senator/Chancellor/Emperor Palpatine.)

Her first bad decision is moving for the vote of no confidence in Chancellor Valorum, leaving the way clear for Palpatine to take power and starting the chain of events that lead to the downfall of the entire Republic.

Her second is the decision to marry Anakin, an immature lad six years younger than herself who has an exceedingly clear superiority complex. (Okay, so maybe we can't control who we fall in love with, but she coulda had a little more sense than to marry him.)

Having married Anakin, she makes the third and necessarily final bad decision: she follows him to Mustafar... and he, finding Obi-Wan had come with her, immediately assumes she knew this and kills her, (albeit "accidentally".)

The penchant for bad decisions apparently is inherited by her son Luke. His bad decision - leaving Yoda on Dagobah to attempt a futile rescue of his friends at Cloud City. He's luckier than his lovely mother, however; he only loses a hand, and, learning from his mistake, he goes back to Yoda, completes his studies and ends up destroying the Empire.

*************

I know there are a million more, but I can't come up with anything right now... my mind went blank! So just two for now... and more later!