What plant (be it shrubbery or annual, vine or bulb) simply won't grow for you?
What specemin simply comes out of the ground, turns brown, and leaves you guessing?
My arch enemy:

Lupines
I've tried it all, be it soaking the seeds, or scarification
I've loved them, amended their soil, kept them cool and watered...and then *poof* they're gone.
What was going to be my tall and stately "Lupine paradise"...
is now a rock garden.
-Paul-