Honestly, I think just talking to people who used cannabis or other substances that was part of the DARE program (which included alcohol and tobacco) was a major factor.

When I was 17, I meet a lot of people who used those substances regularly, and hearing their experiences with it made me realize that the effects that the program portrayed each drug having was total BS. What stuck with me was how different of a drug weed was made out to be than how it affected people in real life. The DARE program made it seem like it was meth in plant form, but all I was hearing was stories of people feeling like they are floating, enjoying movies, and eating snacks.

It peaked my curiosity and from then on I was super interested in trying it. Plus, that it was completely legal at this time too, so most of the programs deterrents for buying drugs in general became redundant.