system
Given the following post, respond as if you're commenting on Reddit:
human
ELI5: Where does the first person each season catch the flu from?

I know the flu is seasonal (influenza flu) - but it HAS to start somewhere each season. Where does that unlucky person catch it? As I understand it, the virus doesn't live too long outside of a human.
gpt
The flu is always going around.  During the summer months, if someone with the flu sneezes outside, the flu virus sprays out from their nose and mouth, and then floats down to the grass where it doesn't get transferred to anyone.

During winter months (flu season), the same sneeze happens in doors where other people come in contact with it, contract the flu and then proceed to spread it further.

tl;dr - the flu virus is always out there spreading, it's just during flu season that humans conduct activities more conducive to spreading the virus.