MAINTAINING YOUR PLANTS:
Fungi & bacteria thrive if the humidity is high. Some not so harmful-to-human chemicals like sulphur can fight them back.
Pests appreciate our
misunderstood efforts to grow food for them. And they can really thrive
in the paradise, we make for them: Plenty of food and no enemies.
Others animals are, at least in the wild, a great help to the plants. Earthworms, bacteria and fungi make compost, while bees birds and mammals fertilizes, ants bring home nutrition and defend the ant-plants, insects feed the carnivorous plants and so on.
Age is just, like for another organisms, a deadly, sexual transmitted disease. You can fight it back with renewing your plants from seeds or cuttings.
Gravity! It may sound odd, but
it is a factor, when you make cuttings of some species of plants. Some
have to lie down to root.
Love! Some people are just
better at growing plants, than others. I have heard that talking to your
plants make them thrive. I think it get down to "timely care". It is
about having the time to observe your plants, water them often, pay
attention to pests, dull leaves and so on.
Other factors, that still haven't been scientific discovered/documented might play a role as well, But I leave that to others to explain.