But I'm also certain that experienced gardeners kill a lot more plants simply because they don't invest as much time trying to resuscitate unhappy plants; not nearly as much time as novice gardeners, who are beset by the agonizing guilt of a plant's failure.
Mistakes don't stop good gardeners, they just make them smarter. They note the failure, remove the victim and move on, ready for the next challenge. A good gardener can sniff out another good gardener pretty quickly by taking a peek at their compost pile or rubbish bin. If there is a half decomposed campanula or a sad penstemon poking out, odds are they're a pretty seasoned and experienced gardener.
Novice gardeners see a sickly plant as a personal failure, a failure of the gardener. Good gardeners don't see it that way, they see the same sickly plant as an opportunity to learn something.
Not only do good gardeners kill lots of plants, they do it more quickly than other gardeners. Beginning gardeners think that they can nurture a distressed plant back to life – even years later they're still trying. They have lots of plants scattered around their landscape that "just aren't doing very well". These plants are in various stages of supposed recovery. But novices hold on to these sickly plants far too long. Suffering mercilessly, these "rescue" plants litter the gardens of the neophytes.