I've spent years as very heavy coffee and/or tea drinker but I have never been addicted to it, either physically or psychologically. I can (and sometimes do!) switch from heavy consumption to going days without it and I don't notice a difference.
In fact, I barely even feel any effects of caffeine at all. Never have.
I’ve know too many people who simply cannot quit smoking, even when it’s clear they’re rotting from the inside out.
Nicotine addiction is on an entirely different level than caffeine.
A single sip of coffee, or a cup of good black tea generally alleviates these symptoms. I had to drink a sip of coffee on day 4 while quitting coffee, and all my headache was gone.
The simplest is that I dislike being dependent on any substance.
A more nuanced reason is that I want to be able to use caffeine as a tool. A cup of coffee is the largest dose of caffeine that I am comfortable taking at any one time. If I already have caffeine tolerance at the level of a daily coffee habit, caffeine has lost much of its utility to me. However, if my tolerance is lower than that, I can really feel it when I do occasionally have use for a cup of coffee (e.g. the day before code freeze.)
Currently my caffeine intake is a cup of tea[0]. This is at the level where I don't hate myself if I miss it[1], and I can still use coffee as a tool on occasion. Also, you can pry my tea out of my cold dead hands.
[0] Note that how much caffeine a cup of tea has is much more nuanced than "black vs green". Cultivar, terroir, steep time are much more important to caffeine levels than how the tea is processed. In fact if anything, green tea cultivars have been shown to have, on average, very slightly more caffeine than black[2].
[1] I feel it, but it's not 3-5 days of migraines
[2] Y. Zuo et al, Simultaneous determination of catechins, caffeine and gallic acids in green, Oolong, black and pu-erh teas using HPLC with a photodiode array detector, Talanta 57 (2002) 307–316
Same here. All my daily coffee drinker friends say coffee has no effect on them. I drink it ~4-6 times a month (when I'm very busy) and I can feel the effects from one cup almost all day. More than two cups actually is quite uncomfortable.
I get weird swings in my caffeine tolerance, so I only consume caffeine 1-2 times a week, or less.
Caffeine can also cause weird mood swings. Its effects are similar to cocaine, just somewhat muted because the delivery mechanism is slower.