Temporal anomaly

[Cinjin]

Currently watching Harry Potter and while in Hagrid's home, Hermione was struck by a carved pebble which she then put into her pocket. Later on she went back in time and threw that same pebble at her earlier self who, as we now, picked up the pebble and put it in her pocket only to later go back in time.. etc. etc..

They did the exact same thing in the movie, Somewhere In Time (Christopher Reeves, Jane Seymore).

The movie opens up with a very old woman bringing a young Christopher Reeves a watch and saying the words, "come back to me".
He later travels back in time only to give the watch to a young Jane Seymore, who of course, was the old woman. Who had the watch first? When was it created?

It's simply a fun way for the writer to increase the "magical fate" factor in the plot line of a movie. Nothing more. Everyone knows that paradoxes make time travel impossible. Why over-analyze an enjoyable film by sitting around ripping apart little details in some futile effort to disprove something that everyone already knows is impossible.

You know how impossibly ridiculous Star Wars/Star Trek is??!? Don't care .... I'd rather just thank Hollywood for entertaining the hell outta me for 30+ years.