Robert A. Heinlein, one of the best Sci-Fi authors out there, wrote a short time travel story called “All You Zombies”. It’s considered to be one of the best of its kind, and it’s a great showcase of the bizarre paradoxes that can result from such writings.

If you don’t want the plot ruined, I suggest you read it first, before continuing.

The story starts out with a young man in a bar sharing a shocking secret with the bartender. And as the story unfolds, full of weird jumps in time, the most bizarre fact is revealed: all the characters in the story (five, basically) are the same person. The young man is the bartender, his own father, and his own mother.

If you still haven’t read it, read it! You know you want to.

And if things remain unclear, read the wikipedia article on the story.