In the original Star Wars trilogy, the distinction between good and evil is stark and uncomplicated. Even in the Han-shoots-first version of Star Wars, it's abundantly clear Greedo was a threat. By the time we get to Return of the Jedi, whatever is supposed to entice Luke to join the Dark Side is a mystery to us, because Luke's status as unwavering hero has been mercilessly cemented.
The Last Jedi is more complicated than that. Its bad guy is ego, which exists in our heroes and villains alike. The Last Jedi then takes it a hundred steps further by tying the audience to the ego, forcing us to experience the characters' failures more acutely than we're probably used to. When we first meet our eponymous last Jedi, Luke Skywalker, he is arguably aligned with the film's detractors: casually tossing his lightsaber off the edge of a cliff, he believes that this garbage has gone on too long and should just die already. He refuses to have anything to do with Rey or any of this new stuff, though he is happy to see Chewie and R2. But he's also a disappointment, to both us and himself, for not living up to the legacy established by the end of Return of the Jedi. His self-loathing affords him the arrogance that he alone gets to decide whether the Jedi live or die, for there will there be no return of the glory days, if there were any glory days in the first place.
Kylo Ren is of particular interest because we feel the pain of his being right. He possesses the same self-importance found in Luke, but never got the same recognition. As in The Force Awakens, Kylo Ren is starved for approval -- which he has never received, either from Snoke (who is always quick to point out his shortcomings) or Luke (who tried to murder him in his sleep). The fact is, Ben Solo did deserve more than he ever got, which is not easy for us to accept in a villain.
This ego-audience melding is chiefly apparent in Poe Dameron. When we first meet him in The Force Awakens, he sasses the bad guy ("Who talks first? Do I talk first?") and eventually goes on to destroy their weapons with his devil-may-care hotshot ways. The Last Jedi begins no differently: sassing the bad guy ("I'm holding for General Hugs?") and defying orders to take 'em out. Except this time, though successful in his attack on the First Order, he gets a lot of people killed. Leia is quick to point out his lack of understanding of true leadership and demote him, and though we're rooting for Poe, we know Leia's right (Leia's always been right). Naturally, we want Poe to be in a position to redeem himself. So when Admiral Holdo shows up out of nowhere (and Poe describes her as "not what I expected"), of course Poe should question her orders! We know Poe is a good guy, and we don't know this Holdo at all! So instead of passing along Rose and Finn's discovery that the First Order has a hyperspace tracker, he keeps it a secret and sends Rose and Finn on a mission to find the "master codebreaker." This plan turns out badly. And it's the second viewing of The Last Jedi in which this becomes painfully clear. We're so tied to Poe that we forget Admiral Holdo has a reputation as an adept military strategist. We're very forgiving of Poe's acts of heroism -- even this last effort that got everyone killed. But just like Poe, our ego is in the way: from nearly every perspective outside of Poe's, Holdo is the war hero, and Poe is the one who got everyone killed yesterday. Holdo and the rest of the ship are sweating bullets to deal with a crisis they only have one shot at, and this belligerent, insubordinate narcissist storms onto the bridge to proclaim he doesn't approve of a plan he only partially understands.
Finally, there's Finn. Finn has a similar arc to Poe's: His own heroic intentions belie an understanding of the bigger picture, but Finn (and the audience) gets his most direct lesson from DJ. After failing to acquire the master codebreaker in the (sorta uninspired but I get it) casino and finding themselves trapped in a holding cell, Rose and Finn meet DJ, a low-rent codebreaker that we know they shouldn't really trust except what other choice do they have. DJ is the ambivalent moral compass of The Last Jedi: He literally tells Finn that there is no clear distinction between good guys and bad guys. Some bad guys are good. Some good guys are bad. He's describing Poe Dameron. He's describing Luke Skywalker. He's describing Kylo Ren. He's describing literally every person ever. And he is, of course, describing himself.
After selling them out to the First Order, DJ explains to Finn, "It's just business."
Finn says, "You're wrong."
But DJ knows the truth. He knows the truth about business, he knows about ego, he knows about morality and the uncertainty of certainty. With minimal hesitation, he gives Finn and Rose - and us - all the codebreaking we require.
DJ is the philosophy of The Last Jedi wrapped up into one single word.
He tells them: "Maybe."