Which constant failures do you still try?

I've grown Brussels for nine years and only had one decent harvest, but perhaps this will be the year? At least the tops never 'blow'! 

Florence fennel is always sad - we might get enough small heads for one risotto, but we also get swallowtail butterfly caterpillars on them, so they are worth the work & the culinary disappointment.

After buying or being given three rhubarb plants I have to accept my baking clay is never going to be their liking. But if somebody gave me a plant I'd try again!!
 
Is there anything you stubbornly refuse to give up on?