I always thought I was one of those people on whom caffeine had little to no effect, since we I was drinking 5 cups a day on average and still felt tired all the time.

During the lock-down I read somewhere that caffeine's half-life in your body is 6 hours. I'd always needed an hour at least to fall asleep at night but I never attributed it to caffeine. So I figured I'd quit coffee for a to see what the effects were.

I can't even begin to tell how big of an effect quitting caffeine had: I routinely fall asleep within 15 minutes of going to bed, I sleep better and longer, I have more energy and one espresso after lunch is enough to stay focused and alert until midnight.