It's a funny word. It stands for solid fact, fidelity, objective knowledge. Things that we believe, beyond the faintest shadow of a doubt, are a part of reality. People have died in the pursuit of it, equally many have dedicated their lives to destroying or distorting it. There are some we consider wise, and full of great truths, and others who wouldn't know truth even if you bashed them over the head with it.
As one might expect, with the Nexus being what it is, truth is just as funny a word there as in real life, perhaps even more so, for being so strange. Cities and empires rise and fall with the same frequency as the sun's routine voyage across the sky. People suddenly exist, and then just as abruptly cease to be just as quickly. Nothing is absolute, and everything is in constant flux. A maelstrom of blood and tears, with no end in sight, and no definite origin.
Meet James Dalton. Just ten minutes ago he had four very simple beliefs, that to him, were absolutely, indisputably, the truth. Firstly, and perhaps most importantly, that hell had finally come to earth. The dead were walking, they were shuffling along in search of human flesh, and weren't going to take no for an answer. The evidence was all around him, of course, and numerous other survivors were in support of this theory, so it clearly wasn't all in his head.
Secondly, Dalton was certain he was going to get out of this hell-hole entirely unharmed. It was a solid fact in his mind. The end had come, and by sheer force of will, he was going to beat it. By gun, by sword, by whatever else he came across in his travels, he would single-handedly take on all comers and rise above all the gore and destruction, triumphant and proud. Of course, this obviously wasn't very likely, and his hubris had already gotten a few other folks killed, but nothing short of death would've ever wrested that idea away from him.
Thirdly, James was, like many other people, under the impression that interdimensional travel was just some sci-fi nonsense, or something that could only happen in the far, far future, and definitely only if a cure to the zombie virus was found. He quite reasonably assumed that the warehouse full of zombies he was cornered in was going to stay a warehouse full of zombies, and no interdimensional portal was going to suddenly change that. As turned the nozzle on his homemade flamethrower, the very last thing he expected was to suddenly find himself in somebody's house, with a family eating a perfectly ordinary dinner on the business end of his flames, instead of the undead horde he'd been expecting.
This wouldn't have been as big a problem, of course, if it wasn't for the fourth of Mr. Dalton's beliefs. The fourth, much to Dalton's delight, was that people and zombies burned exactly the goddamn same. Fire was elegant, beautiful, and absolutely amazing. There wasn't a reason in the world for him to save it for just the dead who got in his way, not one that he could see. Had anyone else been caught in that rift, they would've cut off the wave of kerosene and stopped right after the first accidental casualty. They would've stopped upon realizing the sudden shift in realities, and apologized profusely for killing a little boy. A little boy who, by strange coincidence, was also named James Dalton.
Our James Dalton did not stop, though. He didn't stop to reflect on how he'd suddenly found himself in a whole new world, didn't stop to ask why the family had pointy ears, and sure as hell didn't stop burning things. Not after burning the boy with the same name, not after the boy's little sister, and not when he had turned his crude fire-spouting device on the entire dining room, kitchen, and second floor of the Dalton household. The entire building was little more than a pillar of smoke that evening, because James would not, and could not, be stopped.