I don't know what the cutoff is for a "heavy" smoker - I went through anywhere from one to three packs a day - but I'd honestly say that attitude is 99% of the issue.
attitude towards what, please?
In my case, I liked smoking. I never ever wanted to stop smoking. Not once. Never.
However, I had been smoking
too much in the end of my smoking "career" and I wanted to cut down on smoking
too much, because it was not doing me good.
Compare: I like to eat a piece of chocolate once in my while. But if I were to stuff my face with 2 whole packages of chocolate every day, that would not make me feel good. So I would cut down on eating
too much chocolate. Although I would never ever "quit chocolate" as in stop eating chocolate entirely, for the rest of my life, and never have another bite of chocolate as long as I live.
I made the transition to vaping immediately, effortlessly and with great pleasure as soon as I started up my 1st PV on 4 Nov 2011.
Because I had found a much better alternative. One that gives me all the benefits of smoking (and yes, there are quite a few) without the hazards of the smoke as such.
In my home forum in Germany, it is generally the most inveterate and long-term smokers like myself who make the transition easily. Often to their own surprise. We do not "quit smoking" on purpose. The transition just happens. You know, like the invention of fire? Why eat your meat raw when you can cook it and avoid all the problems with your digestion? Same thing

I am still "eating meat" (consuming nicotine and practising my beloved habit) - but it does not make my stomach hurt any longer.
And it is precisely those people like me, whose transition just happened and who are very happy with vaping, who are the most vocal vaping activists in Europe. Now that we have discovered fire, so to speak, we have no intention of having it banned by greedy, mercenary jerks who are paid by those who treat stomach disorders.
And who say "Fire is dangerous. We will ban it. Eat your meat raw or do not eat meat at all!"