In my own experience, nicotine was not very addictive. As a non-smoker, I started vaping 36mg/ml nicotine in unflavored propylene glycol. I used a high concentration to minimize exposure to any unknown non-nicotine risks. I vaped heavily for about 2 years before getting bored of it. I tapered the dose to zero over two weeks and experienced only mild withdrawal symptoms. It's been about four years since I quit and I've never felt the effects were sufficiently interesting or enjoyable to start again.