Nemesis – Something that a person cannot conquer; the cause of a person's downfall
A nemesis is something that a person cannot conquer; that causes a person's downfall.
Following several near misses (nemesis), she thought she could beat the police, but she couldn't beat them, and the arrest brought about her downfall.
Examples of nemesis in a sentence (cannot conquer)
America's old nemesis, the Soviet Union.
Harry Potter's nemesis, Voldemort.
She saw her nemesis walk away.
Examples of nemesis in a sentence (the cause of a person's downfall)
Have I finally met my nemesis, the IT problem that I'm too old to understand?
Betsy was beside herself with frustration when she heard what mayhem her nemesis had wrought.
Trust is my nemesis.