As Luke stood, looking at the burning homestead and the charred bodies of the only family he ever knew, he had a choice to make. To stay, rebuild, and start over in the same life, or to follow in the footsteps of his father as a Jedi Knight. 

As Anakin stood there, begging Mace Windu not to assassinate the Chancellor, he had a choice to make. Abide by his duties as a husband, to protect his wife, or to fulfill his duties as a Jedi, knowing it might mean doing the one thing he never did unto that point. Fail. 
As Rey stood there, planting her feet into the snow of Starkiller base, staring down the monster that killed the only father figure she ever had, she had a choice to make. To do what she had always done, or to pick up the mantle of the Skywalkers, the blue lightsaber of fate, and fulfill her duty to the memory of Han, to her loyalty to Finn, and to the will of the Force. 

All of these heroes faced the choice. The choice between duty and the easy path. The choice between self and galaxy. The choice between light and dark. 
This dichotomy of duty and choice is fundamental. The mythology of Star Wars simply cannot live without it, as Star Wars is built on the back of all the great mythologies before it, alll of which challenged the heroes to make very similar choices. All of which challenge us to make very similar choices. 
This is explored in every area of Star Wars, from films to television to the written word, duty and choice is a challenge all must face. 

Possibly the most moving (although I admittedly might be a bit bias, as anyone who has listened to the ClashingSabers podcast knows) is Ahsoka Tano choosing to leave the Jedi Order. As she handed over her padawan braid and walked down those steps, she chose the path Anakin could not. She chose the same path that Luke later would. The third path, a path created by oneself. 
Many might see this, at least on the surface level, as choosing yourself over your duty to the galaxy, but that is short sighted. Ahsoka did not choose herself over the Order. She chose the will of the Force, and her duty to it, above anything. We would later see Luke make a similar choice in the throne room on the second Death Star. As he threw away his lightsaber, and proclaimed, “I am a Jedi, like my father before me,” he not only chose his family above himself. He not only chose the light over the dark. He chose, like Ahsoka, to forge his own path. He knew that he could not re-establish the Jedi in the stead of Obi-Wan and Yoda. He had to birth it anew.

The reason the order failed in the first place was because the Jedi could not differentiate between their own desires for power, which they masked as their duty to the Republic, and the will of the Force. If the Jedi were to be reborn, they could not be reborn in the same manner (which is why I believe Luke became a pacifist… but that’s a chapter for another article on another day). 
The Emperor’s entire plan is predicated on this, which is why the Empire is the way it is. He forced the galaxy into a corner that made them believe there was no other choice than war. That their duty was to fight this war, his war, for the greater good. 

The same is true for Anakin. He made Anakin believe that his duty to the Jedi did not matter because they had forsaken their duty to him, that they had failed him by not supporting his love for Padme. 
So when the Empire rises, it is no wonder that its infrastructure is based on giving up your choices, your free will, and choosing duty instead. The stormtroopers are a literal manifestation of this; unlike the clones, who marked their helmets and cherished their individuality, stormtroopers all look the same, giving up themselves to support the Empire. 
Some were able to break from this mold, such as Wedge Antilles and Sabine Wren. They learned the balance between duty and choice. Sabine in particular. While she felt a duty to her family on the Ghost, she also felt a duty to Mandalore and to help save Mandalore from the Empire and the weapon she helped that empire create. It is only when she learns to balance those two loyalties that she is able to make the choice to return to Mandalore and help them towards recovery. 

Some are not able to break from that mold. Ciena Ree’s story is so tragic because of that, as it shows her failing to find that balance. After Alderaan, she knows that the Empire is not what is best for the galaxy, but she is unable to break her bond to that government because of her culture and tradition. She even choses the Empire to the point of being willing to die in a flaming Star Destroyer rather than consider that her duty might be to the relationships she has with others far more than any government. 
In its simplest of terms, that is what duty and choice come down to; not just simply learning how to balance, but what to balance. The key is always choose people (or alien, or whatever term you want to but onto living beings) above anything else. 

That is why Ahsoka walked away, because she chose her duty to the people of the galaxy. The Ahsoka novel paints this picture beautifully, all the way to her deciding that she can best serve people as Fulcrum. 
This is why Luke threw away his lightsaber, and why Rey later picked it up. People she knew, people she loved, need help. That commitment, that bond, is the duty we must choose above all others.