The odds are if you abuse opioids there is a 1/10 or 1/20 I don't recall chance you will consider yourself addicted at sometime in your life. If you have an addictive personality it is likely greater. Don't think of it as "will i be strong enough" but think of it as just rolling the dice with your life. The "Basic Biology of Addiction" thread in the OD Directory linked in my signature might be some good reading for you.
I think that amapola has pointed out something important here that very few people would like to believe and many others will argue over until their dying breath: heroin is addictive, but not more so than other substances. If you don't believe me, go look up alcohol and the rate of alcoholism, the numbers are very much comparable to heroin and heroin addiction. But it
is rolling the dice, and that's scary, because if it comes up "addict..." that's a life-changer right there. That's why I tell everyone I regret trying heroin,
not because I am an addict or I have become an addict (I haven't), but because it was a stupid thing to do in the first place and the consequences far, far outweighed whatever positive experience I might have had.
That being said, I am not a drug advocate of any kind, and I think an individual who
knows that they have an addictive personality should stay far, far away from heroin and all other substances, really.
EDIT: And it's a tough question, and a question that misses the point, to ask "Do you really get addicted the first time?" It's not like anyone call tell you, "It's the fourth time, man, definitely the fourth time that does it..." It doesn't happen that way. Personally, I think it happens once you
make the decision to experiment with the substance; but really, it's something that happens gradually and over time, but you won't know that you're an addict until it's too late, and in that moment, you won't be asking yourself which time "did it," you'll just know that it happened, and you'll wish that you had your life back.