Caffeine effect (please correct me!)

I don't usually drink coffee because I am too sensitive to caffeine. Whenever I drink it, my nerves were over stimulated and thus I couldn't focus on one thing, couldn't sleep until late, and became hard to stay still. I was not a coffee person.

Today, however, I experienced a dramatic effect of caffeine. I drank a half cup of coffee in the morning. With this good amount of coffee, I didn't experience any of the side effects. Instead, I was highly motivated, was able to focus on work, and felt so confident and happy! I like it because I used to be distracted and downbeat, and suffered brain fogs.

Watching a video about caffeine, I learned that caffeine inhibits the adenosine absorption by interfering with adenosine receptors. As a result, it makes us stimulated and happy.

As I have experienced such a great effect of caffeine, I use it some times but not too much because I don't want to be addicted.