More realistic is:
* I go back in time to a November day in 1970.
* I walk past a tall dark haired man in a Navy uniform.
* I accidentally bump into him. The 600 million or so sperm swimming around in his naughties get jostled.
* When he has a passionate night with his wife, a different sperm cell reaches the egg first.
* The sperm that was originally destined to produce me winds up along with 599,999,998 other also-rans.
* I am never conceived, never born, never live, never go back in time, and never prevent my own existence.
* A time paradox occurs.
* The space-time continuum implodes, destroying the universe.
* I go back in time to a November day in 1970.
* I walk past a tall dark haired man in a Navy uniform.
* I accidentally bump into him. The 600 million or so sperm swimming around in his naughties get jostled.
* When he has a passionate night with his wife, a different sperm cell reaches the egg first.
* The sperm that was originally destined to produce me winds up along with 599,999,998 other also-rans.
* I am never conceived, never born, never live, never go back in time, and never prevent my own existence.
* A time paradox occurs.
* The space-time continuum implodes, destroying the universe.