system
Given the following post, respond as if you're commenting on Reddit:
human
ELI5: Why does caffeine sometimes not work in keeping you awake?
gpt
Your brain is filled with keyholes, adenosine is the key that fits to tell you you're tired.

Caffeine has the same shape as this key and fills the keyholes instead, so your body never gets sleepy signals.

If the adenosine has already gotten in the hole, the fake key (caffeine) can't bind.


When you first wake up caffeine is mostly working by causing a small adrenaline boost, same with that 2pm coffee.