Self-sacrifice means doing something for someone else even if it means you might not have something good happen to you.
Here's an example: You and your friend are playing outside when you see a bee. Your friend is allergic to bees, which means if the bee stings them, they could get very sick. You don't want your friend to get sick, so you tell them to run inside while you stay outside and shoo the bee away. You take the risk of getting stung by the bee to keep your friend safe. That's self-sacrifice!
Sometimes, people make really big self-sacrifices. For instance, imagine a parent who works long hours to provide for their children. The parent might be tired and stressed out, but they keep working hard because they want their children to have everything they need to be happy and healthy. It's a big sacrifice, but the parent thinks it's worth it because they love their children so much.
Self-sacrifice doesn't always mean giving up something you want. Sometimes, it's just about putting someone else's needs first. It can be a small thing, like letting a friend have the last cookie. Or, it can be a big thing, like joining the army to protect your country.
Self-sacrifice is something brave and kind people do when they want to help others, even if it means putting themselves in harm's way. It's an important virtue that helps make the world a better place.