Just two simple words, 'what if?' Was all that needed to be asked. This type of question is applied to anything, the most prominent example to me, is fiction. What if's in fiction, is basically, the author creates characters is a world, and asks," What if this happened" and the author will right down the prompt, and have the characters react in their proper ways.
In this story, the world is filled with "quirks". Quirks are magical abilities that appeared out of nowhere one day, just "POOF" and bam! Quirks. But sadly, a small percentage of people in this world haven't formed the magical abilities, they were dubbed as " quirkless" the what if that would probably end up getting presented, would be the main character being quirkless, having their world crash down on them. Their best friend would turn on them, becoming a bully. And in the future, this ex-friend would jokingly tell the boy to jump off the roof. Maybe the character would jump, maybe the boy will punch the bully, maybe he would just leave. Each situation would have a dire consequence. If he jumped, he would either end up dead, head cracked like a broken egg, or something would end up saving him. If the boy punches the bully, the bully might use his quirk once again, might even kill the poor kid. But if he just walks away, he would go under the bridge on his way home, and encounter the slime creature. The slime would try to use his body as a suit, a disguise. The boy would struggle, but due to not having a quirk, he is unable to save himself. In this scenario, two possibilities would arise, the first would be that nobody would save him, and he will die a slow and painful death, and be used as a skin suit. Or, the second, his favorite hero will save him, the hero would try to take off, but the child, in a frenzy, would grab the mans leg, and being lifted into the air, and in the panic, the hero would drop the bottle that held the villan, which would cause the villain to escape, and it would find the bully, and try to use him, and the other hero's would try to help, but due to the boys dangerous quirk, they can't get close to them to save him. With the other boy, they would end up on the roof of a building, where the hero would reveal that a previous villan fight left him crippled, making him be a hero on a time limit. They would part, but both would be at the scene with the villan. Without thinking the quirkless boy would rush forwards, hurling his backpack at the creature, making it recoil at the pain, and the boy would claw, trying to save the other boy, despite the torment he went through due to this boy. The number one hero would save the day, the boy that was captured would be praised while the boy who tries to save him was lectured. Later on, the hero would reveal what his quirk is to the boy, and trains him to be able to use his quirk, the boy eats a strand of the mans hair and gets a power. Later that day he goes to try out for the best hero school on earth, he gets zero point for killing robots, but when the big robot was released, the robot caught a student, and everyone left her, wanting to escape, the boy risked his future at the school to save the girl, he would punch the robot, and break both legs and his arm, the girl would save him, and they both would get into the school.
But what if something else happened, something changed at the very roots of the story, which would cause a chain reaction, a butterfly effect. One little change could make a difference in the story. If the boy was born with a quirk, he would keep his friend, he wouldn't get bullied constantly, he wouldn't be told to kill him self, they might walk home together, and be able to defeat the slime with their quirks, and the boy wouldn't cause the hero to loose the villan, the hero wouldn't get revealed to be on a time limit, and the boy wouldn't get the mans power. At the school he might kill robots. One small change can make a huge difference in the end. A butterfly flapping its wings, can cause a tornado somewhere else in the world