> cannabis half life is anywhere from 1 to 10 days. Considering caffeine's 5-6 hours and fact people usually stay away from coffee after 3PM - it's very realistic to feel cannabis for days after use.
The duration of psycho-effects is not the same thing as the half-life. The half-life of cannabinoids is not too important, as the compounds are absorbed by fatty acids and released slowly over time into the body. The actual high for a typical dose lasts a few hours; you might feel groggy for about a day, maybe two if you're an infrequent user. As for your personal experience, I know people who can function normally in conversation on weed. Personally, I can't, but other things like driving and coordination tasks are no problem for me.