Specifically, a read–write conflict occurs when a "transaction requests to read an entity for which an unclosed transaction has already made a write request.
This could never occur in a serial schedule, in which each transaction executes in its entirety before another begins.
Alice and Bob are using a website to book tickets for a specific show.
Alice signs on first to see that only one ticket is left, and finds it expensive.
Bob signs on and also finds one ticket left, and orders it instantly.