For instance, about 2/3 of the coral bells and tiarella that I plant die; the proportion is probably larger for pulmonaria. But when they do take hold, they grow big and become robust and beautiful. A few species I have given up on; for instance, I have never yet had a Jacob's ladder pull through to the next year. And some plants, such as Solomon's seal, can thrive almost anywhere. But generally, it's a matter of microclimates, I think. I just keep trying until I match the right plant with that microclimate, so eventually I hit a winner. By now I've been doing that long enough that most of my beds are happily filled.
I think there's an analogy to life here, but life conditions aren't as stable as conditions in a garden bed. The target keeps moving, too. Certainly, though, Supergee and Womzilla are the best perennials I have discovered ever! And my job, which flowers well, seems pretty robust and long-lived.