I don't believe in destiny at all. It all boils down to our own choices. People who believe in destiny tend to lose their responsibility and power of will, because they think everything is fixed. When you're drunk you have the choice to step into your car and kill someone or to abstain from driving. It's not destiny if you step into your car and you kill someone. It's your own choice. You can't say "It was destiny that I killed this person with my car". It was a choice that resulted in a crime that needs to be punished.
Just like that, everything is your own choice. It's not destiny that someone is born without an arm, it's just bad luck. It's not destiny that an earthquake happens right before the olympics, it's just bad luck. It's not destiny that humans wage war all the time, it's a choice.