Earlier quoted context omitted.
Did you quit long enough that you got through the withdrawal? Caffeine withdrawal is pretty bad, and you'll probably have trouble thinking. The first time I quit cold turkey, I felt dumb. Couldn't think clearly or focus until I got past it.
How long did it take for you to get past it? TBH I was surprised how bad it is. The first three days I could barely stay awake. No headache though. I managed to do 10 days before giving up. Not sure if that is enough to fully get over it.
Coffee crept back into my life though, the most recent time I cut it out I mixed decaf and regular, decreasing the amount of regular until it was fully decaf over a few weeks. It was mostly smooth, except for one or two steps. I think the week around 50 was bad but still no where near doing to abruptly.