When something stymies you, it stops you from doing what you want to do.
If something stymies you, it is usually frustrating or annoying.
Examples:
The locked door stymies my attempt to enter the room.
Her fear of heights stymies her dream of climbing mountains.
The bad weather stymies our plan for a picnic.
The cat stymies my effort to take a nap by meowing loudly.
The giant rock stymies our progress on the hike.
The tricky riddle stymies the clever fox.