Well this is a complicated question. There are multiple factors.
First, there is the drug itself. We know that some drugs have more "addictive" potential than others; that is, some provide a more "reinforcing effect" than others, which could increase the likelihood that you will try it again.
Second, there is the person. Each individual’s genetic make-up, family history, and personality impacts the likelihood that he or she will keep using a drug and potentially develop an addiction. Also a person's current emotional or physical state (that is whether you are feeling anxious, depressed, in pain, etc.) is a factor too.
Third, there are environmental factors, which in my opinion are what most people underestimate. For example, if a drug is easily available to you, you are likely to use it more often than if it is hard to get. So if it is always around and easy to obtain, or you have friends offering it to you, you might find yourself using it more often.
Similarly, if you use and you don’t get in trouble because your parents don’t watch you closely or they are lenient about drug use, you are also more likely to use more often.
Lastly, it's important that you realize that there are multiple and varying risk factors, and because of that, everyone is at risk.
Read more about the risks of drug use.