Coffee makes you focus better. It’s been scientifically proven. What’s also been proven is that if you think it’s going to help you focus, the likelihood and the amount of focus you get from it increases.
Theoretically, you could fool your body and mind to believe green tea to have the same effect. Or that a designated space makes you focus. Or that having a blanket under your feet while you do your work makes you more efficient.
It’s about using placebos to your advantage.