Life is complex. There are many factors that contribute to how your life will play out. However, there's one thing that will directly impact whether you have a good life or a bad life: your decisions.
Decision-making is a core part of being human. Your life is made up of a bunch of decisions, good ones and bad ones. The more bad decisions you make, the less likely you are to have a good life. The more good decisions you make, the more likely you are to have a good life. For example, kids who continually skip school will arguably be worse off than kids who don't. People who smoke cigarettes regularly will certainly have worse health than people who choose not to smoke. Some situations are black and white and present an obvious ideal decision (e.g. not smoking). Then there are situations when the path and outcomes aren't so clear (e.g. deciding between two colleges). That's when decision-making becomes tough and agonizing.
Your life is completely in your control, and you will be defined by the decisions you've made and continue to make. So it's important to make more good decisions than bad ones, because the bad ones may come with a lot of baggage and stigma that you can't shed.