If Adam and Eve hadn't sinned in the Garden of Eden, do you think that we would still sin ourselves today? Or would everybody, everywhere since then keep from disobeying God? It's hard to guess what would happen, but it would be nice to think that we would not be sinners today, wouldn't it?
Even though we can't really know what would happen if they hadn't disobeyed God, we know that they did. There's a lot of stuff wrong in the world, like people hurting each other or themselves, or confusion about who they really are. All that bad stuff first started happening when Adam and Eve disobeyed God by eating fruit that they weren't supposed to eat (read Genesis chapter 3 for that story).
God did make a way for us to be able to obey Him again, though. That's part of why Jesus came to earth as a baby and died for our sins. If you want to find out more about being saved, you can read the ABCs of Salvation here.