The 102 of this lesson is that, sometimes, the right thing to do will mean hurting someone's feelings. Sometimes, doing the right thing means saying something that can't be said without upsetting someone, even someone you care about, and/or making them feel bad about themselves. Things like setting boundaries can mean having upsetting, uncomfortable, or otherwise unpleasant conversations, and you need to be able to have those conversations, otherwise you are lacking a skillset necessary to, among other things, meaningfully give consent.
You can't go through life without hurting anyone. It's just not possible. Not only are mistakes inevitable, but sometimes, the correct or necessary actions will unavoidably create conflict. Sometimes it's not gonna get to be a mistake. Sometimes, the option that means you don't have to directly hurt someone is wrong. And so you need to know how to navigate a situation in which you have caused hurt, because not every kindness is nice, and not every necessity is kind.