The best answer FX can think of is that drugs are a temporary and dangerous way to avoid dealing with what is going on in your life. Many people take drugs as a way to escape problems they face in their daily lives. The drugs affect their brain in ways that help people to forget what may be bothering them. However, this escape from reality only lasts a very short time, and soon they are faced with the same problems as before. Even worse, the damage drugs did to their brain can very often last a long time. It?s sort of a double-edged sword because not only have you done nothing to solve your problem (the one you were seeking relief from), but now you have also created another problem (the damage to your brain and the potential for addiction).
Also, FX cannot forget that some drugs available to teens now are so strong that they may be addictive, or deadly, the very first time they are used. So, thinking that "only taking a drug once is not a big deal" is very dangerous logic.
In reality, many teens struggle with the exact question that you have asked. Some find it very helpful to speak with a trusted adult, teacher, counselor, or doctor. If you live in Northern New Jersey, you can contact the Adolescent/Young Adult Center for Health at 973-971-6475 for more information
For some more information on why not to use drugs, see some of the other questions in the Alcohol and Drugs section of TeenHealthFX.com. The more you learn about the dangers of drug use, the more likely your question will become: "Why get high on drugs in the first place?"