YY to thinking I had an addictive personality. I've been "addicted" to various games, the internet (still ongoing!), terrible relationships, caffeine, nicotine, but actually when I get bored of these things I just stop with absolutely no trouble at all, well, except for the bad relationships. (Happily married now though.) I've started and stopped smoking several times since I was 18. Currently haven't smoked at all for 18 months. V occasionally miss it, most of the time nope.
It makes so much more sense when I look at it in ADHD terms because it's never been about needing that one particular thing, it's just always about choosing the path which leads to immediate reward and that one thing is a known quantity which gives a good immediate reward.
A good illustration of this - it's obviously more complicated than this but to simplify it down. Our brains have ways of prioritising what's important to us in terms of short and long term gain. A neurotypical brain is able to arrange these goals effectively. So let's say that you decide you want to lose weight, but you are offered a slice of cake.
If you imagine the different choices as being either like a billboard or like a voice talking to you. The "right now reward" is to eat the cake. This billboard or voice might be loud and big and flashy if it's your favourite kind of cake, if you are hungry, if you have a sweet tooth. But on the other hand is the "Later reward" of losing weight and feeling healthier. A neurotypical brain would make this message louder and flashier if the person cares about it a lot. So the neurotypical person when faced with a decision likely has two billboards/voices competing in their head telling them both to eat the cake and to leave the cake. It might be a hard choice but it's definitely doable to stick to the option for later, unless the later board is diminished for some reason, like right now they don't care about later, or unless the right now board is extra bright, like perhaps they are really hungry or they are feeling sad and they know cake will improve their mood. And if the later option is especially important to them, like say they want to lose weight for a big event like a wedding, or because their doctor has told them that it's important, then the "GET THIN" billboard might be extra flashy and important and easily overpower the "EAT CAKE" one.
With ADHD the "Later reward" billboard or megaphone is always faulty. So if you look at your "EAT CAKE" billboard it might be small - if you don't like this kind of cake, if you're not really a cake person, if you are already full. Or it might be medium or big and flashy if you love cake (etc). The same as the NT person's right-now billboard. But the "GET THIN" billboard is always diminished. It doesn't make a difference how much you want to get thin, it doesn't matter if your doctor has pleaded with you that you are damaging your health, it doesn't matter if you have a deadline to lose weight by. This billboard will always be small unless the consequences are something you know will unavoidably happen and that you really don't like. For example, I can always easily avoid eating cheese even though pizza looks delicious and cheesecake as well, because I know for a fact it gives me D&V for 2 days. But I have been known to eat other kinds of food until it physically made me feel sick, because that doesn't register as an unavoidable outcome.
With ADHD to choose a later reward over an immediate one, the immediate one needs to not be that interesting to you OR the consequences of ignoring the later reward somewhat terrible and definite. Otherwise it's just really hard because your brain won't emphasise the later reward for you. You can know 100% what your goal is and why you want to achieve it but you'll always be thwarted because in your head it only ever appears in small print whereas the right now is there in 100-point red illuminated type.
Addiction is slightly different - with addiction the billboard advertising the addicted substance is just enormous and overrides everything so that the addict believes getting their substance/fix of choice is more important than any other thing. An addict for example would just go ahead and steal the "cake" from someone else's plate whereas ADHD does usually have you placing social rules higher than that, especially if it's obvious; you might be unable to resist temptation if you were alone in a public place with some food that didn't seem to really belong to anyone and nobody would find out it's you, but your craving would never be strong enough that it would make you reach across and take it off someone else's plate right in front of their nose, not past young childhood, anyway.
I need to illustrate this with cartoons or something...