You want a step by step guide?
Just kidding, I reckon it develops like any other addiction. The more you do it, the more it becomes a habit, until it finally becomes an addiction. Some really big wins and/or personal problems certainly facilitate the development of a gambling addiction.
+1 I've never been addicted to gambling, but I'm a University student majoring in psychology and this sounds correct. I think an even better way to phrase this is:
"How NOT to become addicted if you invest so much time into the game and trying to improve your skills..."
Addressing how I rephrased it, I believe the key is entirely your mindset. Having solid
bankroll management and discipline is crucial. Bankroll management (or lack thereof) has made or broken more potential poker careers than probably any other factor - and yes that includes running into pocket Aces "that one time."
In my opinion, being prone to tilt and letting emotions get in your way makes you more susceptible to things like a gambling addiction; treating your bankroll and games more like a business with investments is more likely to keep priorities in order.
One last detail I'd like to add though:
"addiction" is not the same as playing a lot - it becomes a problem when it interferes with your day-to-day life in a harmful way. This is greatly perception from the player. A pro like Doyle Brunson might chose to play hours upon hours more poker in their careers than we will ever get close to, but I don't think time invested alone makes this an addiction. Conversely, someone who spends half the time Doyle does with poker might have a gambling addiction if gambling interferes with their mental health, family, relationships and so on.
Many factors contribute to an addiction or not, but I think bankroll management and discipline are perhaps the two greatest barriers against a possible gambling addiction.