Because you're fourteen, those randos are your peer group, and you're stuck with them all day. Also, you're fourteen so you haven't quite figured out whose opinions should be important to you, and also you're wildly insecure about your position in your world.
I'm frankly not a fan of hyperstitious social pessimism. Everyone needs to understand that this isn't knowledge, it's justification.
It's justification for being an asshole to people under the guise of 'helping' them. The people who end up believing it are rubes who do the same to others. Making someone tougher is survivorship bias by another name. It fails to account for the people who don't have supportive family members and friends. It's solution to this is saying, "it sucks, but they just couldn't take it," which does nothing to make things even slightly better for the next person. We're left with those who survived.
Abuse doesn't actually make people stronger. What helps people become stronger is overcoming adversity. You want people to challenge you and to run into obstacles to overcome, but people who are routinely abused just end up far more likely to have mental disorders later. Nobody is better off or "stronger" for having PTSD.
Toxic bosses, colleagues, brutal job interviewers are no where near as violent or persistent or inescapable as childhood bullies and if those toxic people did half the things kids do to each other they'd be quickly arrested and thrown behind bars.
Why would what some random person says break your heart?