Today, over 90% of the global population indulges in some form of caffeine every day. This stimulating molecule evolved from xanthosine molecules to keep plants safe, thriving, and sexually active.
Not only does caffeine act as a natural pesticide, warding off insects with its bitter taste and incapacitating or killing them with its neurotoxic powers (with the exception of the Coffee Borer Beetle, which can survive the human equivalent of 500 espressos), but it also defends plants from competing flora and fungi by stunting their growth.
And there's more. Caffeine-producing plants secrete tiny amounts of caffeine into their nectar. The caffeine boost enhances bees' memories and makes them addicted to caffeine-laced nectar, making them more likely to pollinate the flowers.
While people aren't bees, our brains are similar enough that caffeine has a similar effect on us.