The first time I did heroin I sniffed it, and was high for almost a full 24 hours. I did it with my best friend and we both promised each other "we'll just do it this one time". Needless to say, that didn't happen. I think a lot of people believe heroin addiction is a matter of having a lack of will power or discipline, but it's not at all. Heroin is like tobacco, in that it's a subtle creature that gently seems to work its way into every aspect of your life. At first you think "oh shit, I shouldn't get high before school/work", but then you do it, you can function, and so you do it again. You start to break through all these walls of what was previously unacceptable to yourself to justify and rationalize your drug use. Eventually doing a shot of heroin in the morning will feel as "normal" as a cup of coffee does, only you'll be willing to steal, cheat and lie for this fix.