If you're like me, when you're sick in bed, the last thing you'll want is coffee. By the end of your flu, you'll also have gotten off caffeine and you'll have ascribed the withdrawal symptoms to the flu. Done! Now go buy some decaf :-)
Now I wish I'd never done it in the first place, but here we are.
I think it just comes down to feeling unable to procure the item of your addiction -- and the mental position to want to leave it behind. I couldn't properly quit until that point... pure resolve. Pure resolve, and being stuck in bed in terrible pain for a week (haha?)
I've been burned by getting regular coffees at restaurants and coffee machines when I ordered decaf.
I wonder how hard it would be to have a "litmus paper" style test for caffeine.