Despite not being the First of the Primordials, the Primordial that was to be Malfeas made himself king because he had the gutsto be one. His glorious passion inspired and guided his fellow Primordials, when their mutually incomparable power would have made Asskicking Equals Authority futile. Upon his defeat, the cosmic passion that gave him power and meaning turned toxic. Now, it enslaves Malfeas and randomly subjects him to holocaustic Mania and abyssal Depression. In between these peaks (or torn and stretched out on both peaks at once), his infinite furor is guided by perfect self-hatred, causing him to ceaselessly destroy himself. Bipolar Disorder, among clinically recognized mental disorders, is most likely to end with suicide.
Cecelyne's grandeur is driven by her inadequacy. To fulfill that barren emptiness, she puts on an air of cosmic pomp and importance and cares for her subjects mercilessly and ruthlessly. Her overcompensation (a common pattern seen in those with pathologically Narcissistic Personality) ultimately makes her an empty shell—an infinitely hollow desert, who feels that her value only comes from dominating and being wanted by others. Her powers center around fulfilling others' desires and demanding obedience, but they cannot actually help their user.
As Adrian, she was a literal protector of Creation in that her presence separated Creation and the Wyld. She was selfless and compassionate to an extreme — she gave her own body for her children's safety. She really loved Creation! Gods' betrayal broke her heart to such a painful degree that she is no longer capable of caring about anything, even herself. Her heart was broken so badly that she never put it together again — Adorjan is a victim of Post-Traumatic Stress Disorder, no longer able to express attention in any way other than violence.
The Shadow of All Things may have been a Jerk Ass, but he was a sort of Devil's Advocate — he gave meaning to the world by being its enemy. Now his "virtue" is hollow and the Ebon Dragon displays an extreme form of Antisocial Personality; the only thing he can care about anymore is the suffering he inflicts on others. In the setting of Exalted, Ebon Dragon is one of the extreme few utterly undeserving of sympathy...but, still, the fact that he can't even recognize that he has fallen this low is something to pity.
Other Yozis are pathetic beings in the sense that their current condition inspires sympathy. Kimbery, who once gave herself as life-water and life-blood for Creation, is so terrified of rejection that she destroys whoever approaches her — Borderline Personality. Oramus, the First Primordial, bravely began to fight Pure Chaos and now he, through no fault of his own, is stuck inside his own wings, utterly unable to comprehend the world outside — Schizophrenia. Isidoros, the strongest thing in the universe and all time, lost faith in his own power and withers in perfect, destructivenihilism — Paranoid Personality. Sacheverell was once a visionary who foresaw the ideal future for Creation; now he does nothing but sleep, refusing to feel anything — Dissociative Disorder. The most comprehensible Yozi, Szoreny, has lost control of his ability to mold his personality based on who's talking to him into the ideal Foil, leading to his inability to think straight beyond the short term — Attention Deficit-Hyperactivity Disorder. The fact that every Yozi was struck with a diagnosable mental disorder, turned up to a divine degree, sort of justifies their desire to make everything literal Hell.
Then...we have the Neverborn. Hoo boy. Though not much is known about the Neverborn individually, one can gander at the origin of their morbid hatred — as authors of reality, the Primordials never bothered to put together a scenario where they might die. Without reality being designed to handle their death, the Neverborn could not truly die... but they were still killed and murdered, stuck in a limbo between life and death. The pain of dying has lingered with them for five thousand years. What brought this miserable fate? They were pursing their own happiness in Creation, like every other living thing, before the Primordial War. Even with the most saintly soul, this is more than enough justification for their destructive cause.
Promethean: The Created has a "black hat" group, the Centimani. They embrace Flux, the antithesis to the Azoth that fuels Prometheans. Their powers are the same as those of Pandorans, the natural predators of their kind. Most other Prometheans consider them monstrous (not the least of which because many Centimani hunt other Prometheans to feed their Pandorans). But the gameline makes a point of pointing something out: Prometheans are the embodiment of Blessed with Suck. Any given Promethean is constantly, day-in-day-out, hammered with terrible trials. Being nigh-indestructible is no barrier against the Despair Event Horizon. Most Centimani are less born to evil than dragged to it by the heels.
Specific example: Eve, from Pandora's Book. She was created haphazardly by a selfish Frankenstein who told her to her face that she was just there so he could reach the New Dawn. Then she saw him torn to pieces in front of her, leaving her with apparently no purpose. Other Prometheans taught her that, that wasn't the case, but when she tried to make a new Promethean herself, it failed, spawning Pandorans. Her second attempt worked, but her creation ran off after a few days. Finally, she gave in, creating new Pandorans intentionally so that she'd have something to cling to. Her quote is even, "At least I'm not alone anymore."
From the sample adventure in Magnum Opus, Los Tempestrad. He came to himself in a Hispanic gang's lair, and ended up being a hitman for them for years, and was systematically abused - after all, he was nothing but a puppet, a cheap weapon to be used as Ocho, the gang's leader (and his self-proclaimed creator), saw fit. Then one day, for the first time, he met another Promethean, who took him away from the gang and explained that humans can't create their kind. Unfortunately for him, said Promethean was the manipulative Botherud member Ice Blue, who promptly indoctrinated him in her order's teachings and used him exactly the same way the gang did. His reaction to hearing about Lighthouse, a Promethean messiah supposedly made by a human, is understandable - confused fury, because he loses either way. (If Lighthouse wasn't made by a human, then every other Promethean in Boston is being tricked exactly the way Los Tempestrad was; if a human did make Lighthouse, then Ice Blue has lied to him since they met.) Los Tempestrad is a violent sociopath, but he never had a chance from the day he got off the slab.
In Warhammer 40,000, the Horus Heresy was a galaxy-spanning civil war between the loyal followers of the God Emperor and the traitorous followers of Chaos, shattering the Imperium (from which it still hasn't fully recovered even ten thousand years later) and ultimately dooming the galaxy to a slow, painful death. And yet all of those who rebelled had very legitimate reasons at first, often falling into this trope:
Lorgar genuinely, deeply loved the Emperor, and wanted to have him venerated throughout the galaxy. The Emperor brought the banhammer down on that as soon as he knew about it, as despite being a Physical God he wanted a society of Flat Earth Atheists (due to Chaos being fed by worship). Distraught and suddenly having nowhere to direct his devotion, Lorgar eventually discovered the Chaos gods, who had no problem whatsoever with worship and obeisance. Cue Religion of Evil.
Magnus the Red actually tried to warn the Emperor about the rebellion, yet not only was he not believed, but because he used sorcery to learn and transmit the information he was declared a criminal. The Space Wolves were sent to apprehend him, resulting in the destruction of his homeworld and forcing him to side with Horus, and after the rebellion's defeat other events ensued which turned most of his legion into mindless automata.
Angron first met the Emperor when he was having a Last Stand against impossible odds, even for a Primarch. The Emperor offered to save him, but Angron refused, wanting to die with his soldiers... only for the Emperor to teleport him away anyway, leaving his soldiers to die without him. Angron became even more of a Blood Knight after this, and while fighting wars for him he retained his hatred of the Emperor for many years, jumping at the first opportunity to betray him. It didn't help that he had permanent cybernetic implants that enhanced his rage and prevented him from truly sleeping or having any sort of peace.
Perturabo was an architect by nature and training, and never really wanted anything other than to build beautiful buildings. Then the Emperor took him from his homeworld and hurled him into the Great Crusade, and used his engineering genius to construct defenses the likes of which no-one has ever seen... without ever even thinking to ask what he thought about the whole mess. In the end Perturabo threw in with Horus for the simple reason that Horus was the only individual to ever acknowledge him, not as a demi-god or a tool, but as a person.
The Mage: The Awakening sourcebook Night Terrors: The Unbidden has Alecto, an ananke (a magical construct designed to fulfill a specific purpose) who believes her purpose is to usher people on to their destinies. However, something or someone maimed her in the distant past; she manifests with a broken wing and bleeding, empty eye sockets. And she doesn't realize she's broken; she can't actually remember her real purpose, she just infers it from her powers. She might see an arguing couple, one that would make up in due time, and believe that their destiny is to separate. Her grasp of Fate magic is near-perfect, but it's being filtered through the mind of a severely-damaged being that can't grasp how damaged it is. She drives people to despair and suicide, never realizing she's making mistakes, and in fact incapable of realizing it.
Nualia Tobyn, the Big Bad of the very first Pathfinder adventure, is revealed to be one of these in the adventure details. Nualia is a former orphan from the town of Sandpoint who never knew her parents, and was instead brought up by the local priest. However, because she was an Aasimarnote a human with blood ancestry to angels and other celestial beings, the superstitious people of Sandpoint constantly accosted her, because they believed her grace and divinity would "rub off" on them, forever asking her for favors, trying to take various tokens from her like buttons, cast off clothes, locks of hair, and begged her for blessings despite the fact she kept trying to explain that she couldn't do that. Throughout all this, her adoptive father let it happen — indeed, subtly encouraged it — because he was caught up in visions of the renown he would receive after she went on to be a nun in an order dedicated to his god, and thusly he was incredibly strict with her. When she thought she found a boy who loved her, she gave her virginity to him and became pregnant, only for him to abandon her. Her father became furious and treated her like an outcast when he discovered she was pregnant, and then, when she gave birth, her baby was stillborn and horrifically deformed, because her former swain had unknowingly seduced her in what was actually an old shrine to Lamashtu, goddess of monsters, miscarriages and deformities. Is it really any wonder that all of the above, combined with the psychic emanations from an evil artifact buried under the town, caused her to go insane, murder her adoptive father, burn down his chapel and run away to become a worshipper of Lamashtu, eventually returning to Sandpoint with the intent of murdering its inhabitants to fuel her transformation from an aasimar into a demon?