Purely anecdotal, but for me it was the other way around. Last January, for my New Years Resolution, I kicked my pack-a-day-equivalent e-cigarette addiction. Three to four days of feeling anxious, some weird eating habits, a few headaches, but I still felt fairly productive. In February, I tried to quit coffee. Nonstop headaches for the week, complete inability to keep to a sleep cycle, and the worst irritability I've ever had. (I was at ~3 cups/day prior to quitting) Everyone is different - and some people do have quite terrible caffeine addictions.