I got carried away this spring and spent hours nurturing and growing larkspur and stocks to find them munched or wilting the second I turned my back. On the other hand I lobbed a couple of packets of poppies and night scented stocks on a bare patch in a corner and left them and now have a stunning display with no effort.
Same for perennials - foxgloves and hollyhocks have come up from seed and reliably bring me joy but I either over- or under-prune salvias each year or they just give up after a couple of year. Delphiniums too - they just get slugged and lose the will to try no matter where I put them!
I'd love to know which forgiving plants work for other people. What have you just bunged in and keeps going despite neglect or bad management??