Jedi and Sith - Bad and Good.
Jedi:
Jedis are willing to use their force for defense and goodness for others and they seem to take the self-proclaimed role as the Good guy Police Team of Star Wars, but they're sheer ability to use the force and their knowledge for defense has been their downfall. They don't expose the full potential of the force because they think it's dangerous, and that is why so many Jedi turn Dark because the Jedi think "Hey, the Jedi don't have everything to meet my requirments, so i'll go to darkside to complete the circle". The Jedi hide too many things from their students - including essential force power and knowledge and that's the Jedi Weakness. But their ability to stay pure and serene is what their power is built on.
The Jedi are self-proclaimed Philosophers that need to reflect on their own flaws before playing the Peacekeeper role in the Galaxy.
Sith:
The Sith use their power to exercise their students to become increasingly offensive and aggresive. They train their brotheren to bend the force to satisfy their needs. Their major flaw would be the fact that they guide their students far too fast to become powerful. If you don't know what i am speaking of, heres and example. There is alot of Dark Lords who should still be apprentices. They don't train hard enough because their Egotism has chewed and eaten at them for far too long. And they too are also missing an essential part in the force, being the defensive knowledge and force that isn't trained apon their students.
The Sith are Selfish and mouthy thugs that need to balance their skills and train longer.