Roleplaying games are, in some sense, all about getting to make decisions in the game world that you never get to make in real life. Decisions that are really important. Decisions that can change the course of history.

The PCs are the people driving the story. What they decide to do really matters to the people around them.

As a GM, it's good if you can really underline this point at some stage during an adventure. Make them acutely aware of the import of what they are about to decide. Make it painfully clear that the lives of thousands, or millions, or even billions of people will be affected by this decision. And make it a really tough one. Back the characters into a corner against their morals (alignment is a handy tool here). Throw them on to the horns of a dilemma.

Put them between a rock and a hard place.

Scylla and Charybdis.

Make them sweat.

Make their own safety hang in the balance as well.

And then give them a time limit.

Transcript

Darth Maul: {into phone} Hello? Hello? Damn connection...
Darth Maul: Well, seeya round, kid. I gotta scram.
Obi-Wan: Wait! What does Palpatine want with the Orb?
Darth Maul: I dunno, and frankly I don't care. As long as I get paid.
Obi-Wan: You must know something.
Darth Maul: There was some malarkey about bringing peace to the Galaxy or something.
Obi-Wan: Peace to the Galaxy?
Darth Maul: Look, there's still time to save something from this shemozzle. You're a bright kid. With your partner gone, you could join my firm. I could use someone with your gumption.
Obi-Wan: What about my friends?
Darth Maul: An alien who eats humans? A sociopathic droid? A loony-bin ex-slave kid? Your bozo partner here? They're holding you back. Ya gotta see that.
Obi-Wan: You make a good point. Peace to the Galaxy...
Obi-Wan: I need some time to think about this.
Darth Maul: You got until your fingers give out.